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San Fernando, California, 
Earthquake of February 9, 1971 



LEONARD M. MURPHY 

Scientific Coordinator 



In Three Volumes 




U.S. DEPARTMENT OF COMMERCE 

Frederick B. Dent, Secretary 

National Oceanic and Atmospheric Administration 
Robert M. White, Administrator 

Environmental Research Laboratories 
Wilmot N. Hess, Director 

WASHINGTON, D.C. 
1973 



Volume I 

EFFECTS ON BUILDING si Ki (.1 I Ki.s 

Pari A. Introduction and Buildings 

Part /,'. Buildings continued; Soils and Foundations 

Volume II 

UTILITIES, TRANSPORTATION, AND 
SOCIOLOGICAL ASPEC I S 

Volume III 
GEOLOGICAL AND GEOPHYSICAL sil nils 



I:<h I O) s 

NEIL A. BENFER 

Environmental Science Information Center 
Environmental Data Service, NOAA Washington, D.C. 

JERRY L. COFFMAN 

National Geophysical and Solar-Terrestrial Data Center 
Environmental Data Service, NOAA Boulder, Colo. 

JOHN R. BERNICK 

Publications Services 

Environmental Research Laboratories 

NOAA Boulder, Colo. 

Associate Editor 
LOLA T. DEES 



UDC 550.349.4:62: 69(794) "1971.02.09" 



550.34 


Seismology 


.349 


Earthquake effects 


.4 


Earthquake damage 


62 


Engineering and constiuction 


69 


Building 


(794) 


California 


"1971.02.09" 


February 9, 1971 



For sale by the Superintendent of Documents, 

U.S. Government Printing Office 

Washington, D.C. 20402 - Price $11.90 

Stock Number 0317-0089 



Poit ions of these volumes were prepared under a 
cooperative agreement by the National Oceanic 
and Atmospheru Administration and the Earth- 
quake Engineering Research Institute. 



VOLUME III 

Geological and Geophysical Studies 

CLASSICAL SEISMOLOGY 

SURFACE AND SUBSURFACE GEOLOGY 

VERTICAL AND HORIZONTAL GEODESY 

STRONG-MOTION SEISMOLOGY 

GEOMAGNETISM 



Editors' Preface 



Volume III of this three-volume set contains find- 
ings of geological and geophysical investigations and 
studies that were conducted after the earthquake. It 
includes papers in classical seismology, surface and 
subsurface geology, vertical and horizontal geodesy, 
strong-motion seismology, and geomagnetism. A map 
(pocket insert) of the San Fernando and surrounding 
area shows the locations of many surface breaks and 
effects resulting from the earthquake. Volume I of 
the series describes the earthquake's effects on build- 
ing structures and on soils and foundations. Volume 
II treats utilities, transportation, and sociological 
aspects. 

Disclaimer 

The reports contained in these volumes include 
detailed findings in engineering seismology — particu- 
larly, objective evaluations of causes and effects in 
earthquake damage — and in the seismic and geologic 
characteristics of the physical environment. Although 
derived entirely from the analysis of factual data, 
some of the findings, in a very limited sense, might 
be interpreted as damaging to individual segments of 
business and industry or as being subject to other 
interpretation. 

The scientific papers reflect the interpretation and 
opinions of their authors and do not necessarily 
represent the viewpoints of the National Oceanic 
and Atmospheric Administration or the United States 
Department of Commerce. The United States — while 
providing for the presentation of these papers in the 
public interest and for their obvious informational 
value — assumes no responsibility for any of the views 
expressed therein. The National Oceanic and Atmos- 
pheric Administration's Environmental Research 
Laboratories, in the interest of fulfilling its statutory 
functions, offers these volumes as a forum for pro- 



fessional experts in the fields of engineering seis- 
mology, geology, and geophysics, and for public 
officials charged with the administration of emer- 
gency preparedness and safety programs. 

The National Oceanic and Atmospheric Admin- 
istration does not approve, recommend, or endorse 
any proprietary product or proprietary material men- 
tioned in this publication. No reference shall be 
made to the National Oceanic and Atmospheric 
Administration, or to this publication furnished by 
the National Oceanic and Atmospheric Administra- 
tion, that would indicate or imply — directly or in- 
directly — that the National Oceanic and Atmospheric 
Administration approves or disapproves of the use 
of any proprietary product or proprietary material 
mentioned herein. 



Acknowledgments 



Publication of this volume involved the efforts of 
many individuals. Those who mobilized and con- 
ducted the postearthquake field investigations and 
those who contributed papers are acknowledged 
throughout the volume. Christopher Rojahn, of 
NOAA's Seismological Field Survey, San Francisco, 
Calif. — who served as a NOAA liaison representative 
with the Earthquake Engineering Research Institute 
— assisted in the compilation of manuscripts and 
illustrations. Among the many persons who assisted 
in the technical processes of publishing this vol- 
ume, the editors express their special appreciation 
to Lola T. Dees, Lila V. Paavola, and Gabriel J. 
Bren for help in editing the volume; to Edward W. 
Koehler, NOAA Publications Officer, and William E. 
Kusterbeck for printing and production assistance at 
all stages; and to John L. Cooke of the U.S. Govern- 
ment Printing Office for designing and guiding the 
publication through the final stages of production. 



Digitized by the Internet Archive 

in 2013 



http://archive.org/details/sanfernandocalifOObenf 



Contents 



Page 

Editors' Preface , v 

Introduction: Leonard M. Murphy 1 

Classical Seismology: 

Historical Seismicity of San Fernando Earthquake Area: Charles F. Richter . . 5 

San Fernando Earthquake: Seismological Studies and Their Tectonic Implica- 
tions: Clarence R. Allen, Thomas C. Hanks, and James H. Whitcomb .... 13 

Felt Area and Intensity of San Fernando Earthquake: Nina H. Scott 23 

Focal Mechanism of San Fernando Earthquake: W. H. Dillinger 49 

Seismograms, S-Wave Spectra, and Source Parameters for Aftershocks of San 

Fernando Earthquake: Brian E. Tucker and James N. Brune 69 

Increased Seismic Shaking Above a Thrust Fault: Robert Nason 123 

Surface and Subsurface Geology: 

Map of Surface Breaks Resulting From the San Fernando, California, Earth- 
quake of February 9, 1971: A. G. Barrows, J. E. Kahle, F. H. Weber, Jr., and 
R. B. Saul 127 

Effects of San Fernando Earthquake as Related to Geology: R. F. Yerkes .... 137 

Subsurface Geology of Portions of San Fernando Valley and Los Angeles Basin: 
J. A. Johnson and C. M. Duke 155 

Subsurface Investigatioji of Ground Rupturing During San Fernando Earth- 
quake: Edward G. Heath and F. Beach Leighton 165 

Trench Exposures Across Surface Fault Ruptures Associated With San Fernando 
Earthquake: M. G. Bonilla 173 

Plane table Survey of Parking Lot Damaged by San Fernando Earthquake: James 

B. Pinkerton and Jane M. Buchanan 183 

Ground Displacement at San Fernando Valley Juvenile Hall During San Fer- 
nando Earthquake: Richard B. Fallgren and Jay L. Smith 189 

Ground Movements in Van Norman Lake Vicinity During San Fernando 
Earthquake: T. Leslie Youd 197 

Earth Rupture and Structural Damage by San Fernando Earthquake in North 

Sylmar Housing Development: Donald O. Asquith and F. Beach Leighton . . 207 

Geology, Earthquake Damage, and Water Table Fluctuations — Metropolitan 
Water District Facilities, Sylmar Area: Metropolitan Water District of 
Southern California 213 



vn 



viii Contents 

Vertical and Horizontal Geodesy: 

Land Movement Studies Related to San Fernando Earthquake Department of 

County Engineer, County ol Los Angela 

Horizontal Crustal Movements Determined From Surveys Aftei San Fernando 
Earthquake: Buford K. Meade and Robert W. Miller 

Vertical Crustal Movements Determined From Surveys Before and After San 
Fernando Earthquake: Ninny I.. Morrison 

Strong-Motion .Seismology: 

Strong-Motion Accelerograph Records: R. P. Male) and W. K. Cloud 

A Statistical Summary of Accelerograph Performance: R P. Maley 

Seismoscope Results: Ii. J. Mod ill 

Strong-Motion Accelerogram Processing: I). E. Hudson 365 

Analysis of Pacoima Dam Accelerogram: M. 1) rrifuna* and I) E. Hudson . . 75 

Velocity Response Envelope Spectrum as a Function of 'lime: Virgilio Perez . . 393 

Response of Pacoima Dam to Aftershocks of San Fernando Earthquake: W. V. 

Mickey, V. Perez, and W. K. Cloud 403 

Geomagnetism: 

Repeat Magnetic Field Survey of San Fernando Faith quake Fpicentral Area: 

J. E. O'Donnell and H. E. Kaufmann 417 

Index 423 



Introduction 



LEONARD M. MURPHY 

Director— Seismological Investigations Group 

Earth Sciences Laboratories 

Environmental Research Laboratories, NOAA 



In Volume III, studies of classical seismology, sur- 
face and subsurface geology, vertical and horizontal 
geodesy, strong-motion seismology, and geomagnetism 
make available a vast source of physical environ- 
mental data about the San Fernando earthquake. 
These studies provide the scientific input for further 
evaluation of structural damage to buildings, dams, 
towers, highways, bridges, and multipurpose facilities 
of utility companies as described in Volumes I and II. 
Many of these studies must be considered preliminary 
in their findings because of their early publication, 
which did not permit sufficient time to conduct 
detailed analyses. It is anticipated that the results of 
many additional investigations on the scientific 
aspects of this earthquake will appear in future 
publications. 

In a review of the seismicity of the San Fernando 
area, C. F. Richter describes the events that appear 
to be most significant with reference to past earth- 
quake activity and probable future earthquakes in 
the affected area. Included in the descriptive list 
are 28 earthquakes dating from July 28, 1769, 
through July 16, 1965. He singles out the Pico 
Canyon earthquake of April 4, 1893, which had a 
center of disturbance that was somewhat farther west 
and a magnitude that was probably less, for com- 
parison with the San Fernando earthquake of 1971. 
The hypocenter of the San Fernando main shock 
(34°24.7 , N., 118°24.0 / W., h = 8.4 km), 55 aftershocks 
of magnitude 4.0 and greater through December 31, 
1971, and their tectonic implications are discussed by 
C. R. Allen, T. C. Hanks, and J. H. Whitcomb. Al- 
though it is dangerous to attempt to draw conclusions 
about possible migrations in aftershock activity with 
time, it may be significant that all of the larger after- 
shocks that were located in the southwestern ex- 
tremity of the aftershock zone — near Chatsworth and 
Granada Hills — occurred relatively late in the after- 
shock period. The basic mechanism of the initial 
faulting was that of a thrust fault which had a strike 



1 



2 San Fernando Earthquake of 1971 



of about N.70 AW, a dip ol aboul 50 M , and a 
significani component ol left-lateral slip in addition 
to the tin list component. 

N. H. Scoti reports Modified Mercalli intensities 
ranging from VI I IX I ovei an area ol approximately 
190 square miles and a "generally felt" area of 80,000 
square miles. The maximum intensity of XI is as- 
signed to the Olive View Hospital in the northern 
Sylmar area. Intensities <>l IX X are indicated in 1 1 x- 
Sylmai San Fernando area. The detailed summaries 
of the effects were compiled from 2,000 reports re- 
ceived through the earthquake questionnaire card 
canvass and many preliminary releases prepared 
shortly alter the earthquake. This detailed compila- 
tion of earthquake effects by Scott, the special studies 
appearing in this volume, and those in Volumes I 
and II, provide the most comprehensive catalog ol 
such data for any United States earthquake since the 
great San Francisco earthquake of 1906. 

W. H. Dillinger, studying both P- and S-wave data 
from over 170 seismograph stations throughout the 
world, considers the local mechanism of the main 
shock. His results give one plane with strike N.65°W., 
dipping 55°NE., and a second plane with a strike 
N.40°W., dipping :57.7°SE. 

In a study of 167 aftershocks (M L =i/2 to 4i/£) , 
B. E. Tucker and J. N. Brune report that the char- 
acteristics of the .S-wave spectra apparently represent 
seismic source properties, giving seismic moments of 
10 18 to 10" dyne-cm, source dimensions of 50 to 
500 m, and stress drops of 1 to 300 bars. An apparent 
upper value in stress drop (more than an order of 
magnitude greater than stress drops previously re- 
ported for small earthquakes) may represent the 
regional effective stress, while the range in stress 
drops may correspond to a range in fractional stress 
drops. 

Two possible mechanisms, the effects of uncon- 
fined elastic-strain release above a thrust fault and 
multiple reflection of seismic waves at the thrust 
fault, are offered by R. Nason as explanations for 
increased shaking above an earthquake thrust fault. 

Detailed field mapping of the geology and surface 
effects of the earthquake by the California Division 
of Mines and Geology are reported by A. G. Barrows, 
J. E. Kahle, F. H. Weber, Jr., and R. B. Saul. They 
discuss surface faulting, surface effects other than 
faulting, the Granada Hills aftershock of March 31, 
1971, and findings from a series of backhoe trenches 
dug across surface features. A map, prepared by the 



California Division ol Mines and Geology ''and in- 
cluded in the pocket inside the- ba i of this 

volume, , depicts the many suilacc- effects of the 

eai thqual e. 

In describing the effects ol this earthquake as re- 
lated to the geology, K F. Ye-rkes states that the 
permanent deformation accompanying the faulting 
iik hided: an cast trending /one of tectonic ruptures 
thai liaveise the- urbanized vallcv floor and that co- 
incide with evidence of prior faulting; uplift, tilting, 
and SOUthwestward shifting of an area ol more than 
75 scju.ne miles of the southwesternmost San Gabriel 
Mountains; and numerous slope failures. 'I he San 
Fernando fault is not known to have ruptured pie- 
viouslv dining Instoiie time and. although segments 
ol the fault had been mapped, no evaluation of their 
potential activitv had been attempted. Abundant 
evidence- ol geologically iceeiit faulting along the 
same trend indicates the- activitv ol the zone. 

|. A. Johnson and G. M. Duke describe the sub- 
soil. i<e geology of portions of the San Fernando 
Valley and Los Angeles Basin. A generalized geologic 
map shows the major rock tvpes in the area and their 
relationship to topographic and geologic featut' 
the subsurface investigation of ground rupturing dur- 
ing this earthquake, F. G. Heath and F. B. Feighton 
examined 14 trenches ranging from 6 to 14 feet in 
depth. They give detailed information for each 
tie in h and related tectonic events along the Tujunga 
and Sylmar segments of the San Fernando fault. The 
subsurface trenching demonstrates that faults can be 
observed and mapped in test trenches, but commonly 
two or three trenches must be located along a sus- 
pected fault zone to establish with certainty the 
presence or absence of faulting. Further information 
is presented by M. G. Bonilla based on detailed study 
of four trenches, seven other trenches examined in 
reconnaissance, and trench data provided by others. 
Trenches at a particular project site may not reveal 
diagnostic relations despite use of the best judgment 
in locating the trench. Realistic evaluation of the 
activity of a fault usually requires consideration of 
data obtained well outside the confines of a particular 
site. 

A planetable survey of a severely damaged paved 
parking lot is described by J. B. Pinkerton and J. M. 
Buchanan. The survey, which made it possible to 
compare postearthquake maps of the parking area 
with preearthquake maps, was part of preliminary- 
work to determine the amount and direction of dis- 



Introduction 



placement across the Sylmar segment of the San 
Fernando fault zone. 

Ground displacement at the San Fernando Valley 
Juvenile Hall was investigated by R. B. Fallgren and 
J. L. Smith. They note that damage to the facility 
resulted from severe shaking and differential ground 
movement. The permanent ground displacements 
near the Juvenile Hall are the result of settlement 
and gradual migration of soft soils downslope in a 
zone of narrow lateral extent during the earthquake. 
The zone exists here as the combined effects of the 
selective deposition of soft soils in a lowland or 
trough formed by coalescing alluvial fans in a bed- 
rock depression, near-surface ground water, and past 
displacements of similar nature in the same area. 
T. L. Youd studied the origin of ruptures and dis- 
placements in the Van Norman Lake vicinity. The 
results show that differential displacements were 
smaller outside rupture zones than inside and that 
relative horizontal displacements within rupture 
zones were downslip and generally several times 
greater than corresponding vertical displacements. 

Earth ruptures and structural damage in a north 
Sylmar housing development were studied by D. O. 
Asquith and F. B. Leighton. The investigation con- 
sisted of two phases, a surface mapping phase, 
followed by a subsurface exploration. Results are 
presented for damage to construction caused by 
ground rupture and not associated with ground 
failure. 

The Engineering Geology and Survey Branches of 
the Metropolitan Water District of Southern Cali- 
fornia, which has been investigating the Sylmar- 
San Fernando area since 1962, presents information 
on the geology, earthquake damage, and fluctuations 
of ground water levels. 

The Geodetic Section of the Department of 
County Engineer, County of Los Angeles, reviewed 
the work of 1 1 agencies that conducted geodetic 
measurements in the earthquake-affected area and 
reported on horizontal and vertical land movements 
resulting from the earthquake. Based on preearth- 
quake and postearthquake constrained values, the 
greatest movement of a first-order horizontal control 
station was at Pacoima L-l — with a movement of 
6.35 feet N.69°W. The greatest elevation change 
of a precise bench mark was +4.72 feet at BM 
03-00820 — located near the intersection of Foothill 
Boulevard and Hubbard Street. B. K. Meade and 
R. W. Miller report in great detail, and with exten- 



sive observational listings, the results of horizontal 
crustal movements measured by the National Geo- 
detic Survey of NOAA. Results were adjusted by 
holding: (1) one position, station Cahuenga 2, fixed; 
(2) all stations along the outer rim of the net fixed 
between surveys; and (3) fixed certain stations along 
the western side of the net. N. L. Morrison presents 
the magnitude and extent of vertical crustal move- 
ments, determined by comparing the results of level- 
ing surveys before the earthquake and special surveys 
after the earthquake. 

Fortuitously, the earthquake occurred at a time 
when several hundred strong-motion seismographs 
were operating in the Los Angeles area. Abundant 
unique acceleration data from 241 accelerographs 
located at distances of 8 to 369 km from the earth- 
quake's epicenter are reported by R. P. Maley and 
W. K. Cloud. They present detailed information for 
145 accelerograms. Maximum horizontal accelerations 
of 1.25g and maximum vertical accelerations of 0.72g 
were recorded at the abutment of the Pacoima Dam, 
8 km from the epicenter. R. P. Maley, in a separate 
paper, gives an account, and statistical summary, of 
accelerograph performance. Seismoscope records ob- 
tained from 144 instruments, as reported by B. J. 
Morrill, are a valuable complement to the accelero- 
graph records. 

D. E. Hudson describes the processing of strong- 
motion accelerograms by the California Institute of 
Technology Earthquake Engineering Research Lab- 
oratory in Pasadena. In view of the unusual potential 
usefulness of the Pacoima Dam accelerogram to the 
scientific and engineering profession, M. D. Trifunac 
and D. E. Hudson provide details of the site geology 
and operating condition performance and calibration 
of the instrument. They conclude that the instrument 
performed essentially to specifications and the re- 
corded acceleration traces may be adopted as repre- 
sentative of the actual motion of the instrument 
foundation. Integration of the digitized accelerogram 
indicated tilt during the first 10 to 15 seconds after 
it was triggered. Comments are offered about the 
computed relative velocity and displacement spectra 
with a concluding statement that response spectra 
curves alone cannot give a complete picture of the 
effects of the time duration of the acceleration 
history. V. Perez analyzes response spectra at 5 per- 
cent of critical damping for five accelerograms and 
concludes that the maximum relative velocity re- 



A San Fernando Earthquake o) I'fl I 

spouse spectrum is not necessarily caused by the W. K. (loud, who comment on the frequency-domain 

maximum ground acceleration and the maximum amplification and time-domain amplification of the 

velocity response is not necessarily proportional to seismu signals. 

maximum acceleration. The response of the Pacoima In the concluding report, J. J O'Donneil and 

Dam to eight aftershocks, as recorded ai three sta- H. E. Kaufmann compare the magnetu field sui 

tions that were installed at the dam to record after- made aliei the San Fernando earthquake and the 

shocks, is reported by W. V. Mickey, V. Perez, and repeal survey ol April I to 7, \'fi'l. 



Historical Seismicity of 

San Fernando Earthquake Area 



CHARLES F. RICHTER 

Seismological Laboratory 
California Institute of Technology 
Pasadena, Calif. 



This contribution lists and briefly describes the 
past events that appear to be the most significant 
with reference to past earthquake activity and future 
probabilities for the area most affected by the San 
Fernando earthquake. That area is considered to in- 
clude the western and central parts of the San Fer- 
nando Valley, the mountains north of it, and envi- 
rons of Newhall, Saugus, and Castaic. 

Earthquakes listed are of four main types: (1) 
Those originating within the given area; (2) those 
reaching notable intensity (sometimes damaging) 
within it, but centered outside; (3) large earth- 
quakes with distant center, but including the given 
area within the range of shaking perceptible to per- 
sons; and (4) disturbances of uncertain origin or 
character, which may or may not have affected the 
given area. 

Magnitudes are given only for earthquakes which 
were recorded by seismographs; prior to 1930, such 
data are incomplete and imperfect. To reduce confu- 
sion, local intensities are not given in numerical 
form, as with the Rossi-Forel or the Modified Mer- 
calli Intensity Scale, but are cited only in descriptive 
language. 

Because of the great difference in the amount and 
reliability of information available in earlier and 
later years, the reader is earnestly advised not to use 
this list for statistical purposes or to search for cycles 
or periodicities in occurrence. Any such studies 
should be based on thorough critical study of the 
much larger body of historical and instrumental data 
from which the following items are extracted. 

Most of the given area was thinly populated until 
comparatively recent years, and the mountainous 
part of the area is still unsettled. Historical data are 
often incomplete and fragmentary. 

The present listing does not include earthquakes 
that affected the given area only in its southeastern 



(i San Fernando Earthquake of 1971 



part, namely, the southeast end ol the San Fernando 
Valley, including Burbank and Glendale; noi 'Iocs ii 
include earthquakes ol interest mainly foi the effects 
in the centra] pari ol Los Angeles. In general, earth- 
quakes originating cast ol Los Angeles are omitted; 
among others, iliis cx< ludes a numbei ol moderate to 
major earthquakes on the San Andreas 01 San [a 
cinto faults, sue h as those ol July 22 and Decembei 
25, 1899,April21, 1918, and July 22, 1923. 

California earthquake history begins with the Insi 
Spanish land exploration in 1769. The mission at 
San Gabriel was founded in 1771, and the pueblo ol 
Los Angeles was established in I7N1. 

The mission ol San Fernando Rcy de Espafia was 
founded in 1707; until the 20th century, the small 
town of San Fernando, which grew up near it, was 
the only noteworthy center ol population in the 
western San Fernando Valley. The eastern end ol the 
valley developed gradually toward the end of the 
19th century, with Burbank and Glendale as suburbs 
of Los Angeles. 

The northern towns of Xewhall and SaugUS are ol 
older date, having benefited by early discovery of 
gold and by oil developments. Entry of the railroads 
in the 1880s added small settlements near some of 
their stations. 

Major changes followed the bringing in of water 
from the Owens Valley by aqueduct in 1913. Several 
new towns were laid out at that time. Some of their 
names have changed; what were originally Lanker- 
shiin and Owensmonth are now North Hollywood 
and Canoga Park. 

As lor instrumental installations, the first continu- 
ous earthquake recording in southern California 
began in 1906 at Point Loma (near San Diego) , 
with equipment of relatively low sensitivity. Compa- 
rable instruments, or better, had been in operation 
at Berkeley since 1887, but contribute little to our 
data on earthquakes in southern California. Modern 
seismographs began recording in 1910 at Berkeley 
and in 1911 at Mount Hamilton (Lick Observa- 
tory) ; bulletins for these stations show useful entries 
for large earthquakes in the south. 

A new period of recording and cataloging ensued 
with the setting up of a seismological program, head- 
quartered in Pasadena, under the auspices of the 
Carnegie Institution of Washington; Harry O. Wood 
administered the program as its chief. Regular re- 
cording began in Pasadena in 1923; it was comple- 
mented by stations set up in 1926-27 at Riverside, 



Santa Barbara, and La folia and in r line- 

maha and Haiwee m Owens Valley. 1 his net 
was extended gradually through ttu and now 

included 15 routine stations. In 1937 administration 
ol the program was taken ovei by the California In- 
st itute ol 1 e( hnoloj 

Entries foi individual earthquakes follow. 

17o ( ) July 28. The fust credibly documented Cali- 
lomia earthquake was experienced by the exploring 

party ol Gaspai de Poitol.i when encamped on the 
Sania \na Ri\ci not In from the site ol the pr< 
town ol Oli\c. Light aftershocks were- noted by the 
party dining the following clays as it proce 
westward. Speculation is open as to where the epi- 
( entei may have been, but it is unlikely that it was in 
the- San Fernando earthquake area. One- would 
rathei suspect the Whittier, Norwalk, Elsinore, or 
San | k mto fault Origin on the San Andreas fault 
is less likely, but not altogethei to be exc luded. 

Note; Small earthquakes were so frequent in the 
San Gabriel Valley in the immediately following 
years thai Fathei Sena referred to it as el voile de los 
temblores. 

IS12 Decembei 8. This earthquake destroyed part 
ol the mission (lunch at San (nan Capistrano; it was 
seriously damaging at San Gabriel, but apparently 
not at San Fernando. The same faults named in rela- 
tion to the 1769 earthquake might be considered also 
for this event. 

1812 December 21. This major earthquake usually 
is supposed to have originated under the Santa Bar- 
bara Channel, partly because of some reports (which 
have been questioned) that it caused high waves 
along the coast. It destroyed the mission at Purisima 
(near Lompoc) . and more or less damaged those at 
Santa Ynez, Santa Barbara. San Buenaventura, and 
San Fernando. 

Note that California historical material of all 
kinds is scanty for its Mexican period, particularly 
from the disestablishment of the missions, which 
began in 1834, to the American acquisition in 1848. 

1S52 November 26. Strong shaking over a large 
part of southern California. Probably a major earth- 
quake; possibly more than one event was involved. 
Heavy shaking is reported for San Simeon. Los An- 
geles, and San Gabriel, but the most interesting item 
is the reported opening of fissures for at least 30 
miles in Lockwood Valley. The valley of that name 
in Ventura County is on the course of the Big Pine 



Historical Scismicity of Earthquake Area 



fault. (There is a Lockwood in southern Monterey 
County, but it is unlikely that tins is intended.) 

185 s ) July 10. Strong at Los Angeles, where it 
seems to have caused more damage than the great 
earthquake of 1857 (see next entry). Bells at San 
Gabriel Mission were thrown down. The Hugo Reid 
adobe, located almost directly on the Raymond 
fault, was wrecked. 

18^7 January 9. This event was the earliest of 
three known great shocks accompanied by faulting in 
California. Displacements occurred along the San 
Andreas fault, extending probably from Carrizo 
Plain in San Luis Obispo County southeast to a lo- 
cality in San Gorgonio Pass, northeast of Banning. 
This event often is termed the Fort Tejon earth- 
quake because of strong shaking at the fort, then the 
point of habitation nearest the fault; nearly all the 
buildings were thrown down. In the town of San 
Fernando, several houses were thrown down; the 
roof of the mission church of San Buenaventura col- 
lapsed; all the houses in Santa Barbara are reported 
to have been damaged. 

1872 March 26. The second great California earth- 
quake caused faulting in Owens Valley along a belt 
including the east base of the Alabama Hills. Heavi- 
est damage and casualties were at Lone Pine where 
27 were killed. The shaking was perceptible, but not 
violent, in and about Los Anoeles. 

1879 August 10. Light shock at Los Angeles. Re- 
ported as "quite severe" at San Fernando, whatever 
that means. 

1893 April 4 (Tuesday) . This, the Pico Canyon 
earthquake, is of great interest for comparison with 
the 1971 event. The same general area was heavily 
shaken, but the center of disturbance appears to 
have been farther west, and the magnitude was prob- 
ably less than in 1971. Nearly all the accessible infor- 
mation appears in Edward S. Holden's Catalog of 
Earthquakes on the Pacific Coast, 1769-1806; it is 
here transcribed in full, with slight rearrangements, 
omitting only (1) Holden's assignments of intensi- 
ties on the Rossi-Forel Scale following each individ- 
ual item, which add nothing to our knowledge of the 
earthquake, and (2) reported times of occurrence. 
There was evidently only one large shock, for which 
the time is stated variously from 11:40 a.m. to a few 
minutes after 12 noon; these differences can only 
represent imperfect observation or inaccurate timing 
due to clock error, etc. The earliest reported times 
are probably most nearly correct. 



Mojave: "This place was visited by four distinct 
shocks of earthquake. Buildings were rocked for sev- 
eral seconds, creating considerable fright. At Saugus 
chimneys were knocked down and dishes and other 
household furnishings were broken. The impression 
is that the shock came from the northeast." 

San Bernardino: "A heavy earthquake, moving in 
a southeasterly direction. No damage." 

Santa Ana: "A slight earthquake was felt, the 
movement seeming to be from west to east. The vi- 
brations were so slight, however, that many people 
were not aware there had been any disturbance of 
the earth's surface." 

Los Angeles: "There was a slight earthquake of 
short duration. The movement was from west to 
east. In observer Franklin's office the barometers 
were well shaken, and continued to oscillate percep- 
tibly for 2 minutes at least. It lasted about 18 sec- 
onds." 

San Diego: "A slight shock. It was felt only in the 
upper stories. It shook the barometer at the signal 
office." 

Duarte: "Light shock, east and west." 

Ventura: "Heavy." 

Nordhoff: "Heavy." (Xordhoff is now Ojai.) 

Los Angeles: Newspaper account of April 8: 
"Alarming reports of seismic disturbances have just 
been received from the oil region of Newhall, 35 
miles from this city. Dating from last Tuesday, the 
day on which Los Angeles experienced a slight 
shake, there has been a terrifying series of temblors, 
accompanied by subterranean explosions. These dis- 
turbances have been frequent, and have been accom- 
panied by landslides from the mountains of an 
alarming and dangerous description. A letter dated 
from Pico Canyon, about 8 miles southwest from 
Newhall, reads substantially as follows: 'I was driv- 
ing this morning when my horse became frightened 
without apparent cause, and there came a rumbling 
sound which grew terrifying. I looked up and saw an 
awful sight. Landslides from every peak in sight 
came tumbling down, with hu°:e boulders. The 
mountains appeared as if myriads of volcanoes had 
burst forth. When I got to the long bridge I saw Mr. 
Thomas standing dazed, holding to the railinsr, and 
others came running across the bridge. The earth 
opened in a number of places and the scene was in- 
describable. Men cried, prayed, and swore. When I 
reached my house I found everything upset. Pictures, 
dishes, and everything breakable were smashed, and 



8 San Fernando Earthquake of 1971 



two stoves were broken all to pieces. All the aftei 
noon lightei shocks continued, and also through the 
night.'" Anothei lettei dated on Friday, April 7, 
says: "On Wednesday night, jusi as I had gon< to 
bed, 'Crash!' came another great shock. All night 
long they recurred, keeping up until morning; and 
all day Thursday ihey continued, each preceded by a 
heavy subterranean explosion. The house the fore- 
man lived in was demolished this lime. Last night 
was less exciting, and at 8 o'clock this (Friday) 
morning we had another, which was fully as terrify- 
ing as the first. The shocks were worse in the canyon 
here than elsewhere, hut al Newhall and all aiound 
this part of the c ounty they have been tei i dying." 

Los Angeles: Newspapei account o| April 9. "The 
San Fernando range of mountains, where the greatei 
disturbance took place during the week, weie pretty 
generally shaken up every clay, beginning with I ues- 
day. The last temblor, a slight one-, was felt in the 
canyon about 10 o'clock Sunday night. There were 
no shocks so severe as the first one, and they grad- 
ually lessened in lone and frequency. As far as can 
be learned the area of the tremblors was not confined 
entirely to the San Fernando Range, but dipped 
across the big Newhall ranch, past Saugus and over 
into the Castac [Castaie] and Pirn mountains, north 
of Newhall. Strange as it may seem, although New- 
hall is only 8 miles from the Pico Canyon, where 
the shakes were more continuous than elsewhere, the 
people in that town did not feel many of them. 

"The greatest disturbance was in and around the 
oil wells of the Pacific Coast and San Francisco com- 
panies at the head of Pico Canyon. Mintryville is a 
little town with a schoolhouse, and is the residence 
of the superintendent of the oil companies. Scattered 
about are pretty little cottages, the homes of employ- 
ees. 

"One who has not visited the peculiarly formed 
canyon can hardly have a clear conception of the 
consternation with which the earthquakes were re- 
ceived by the 130 people who live in this vicinity. 
Temblors that would, as these did, tilt up great oil 
tanks full of oil, detach immense boulders from the 
mountainsides weighing tons, and cause big surface 
fissures in the ground in various places, are not cal- 
culated to make people rest well at night, and when 
these disturbances continue at irregular intervals for 
5 days it is a wonder that the women and children in 
the canyon bore the ordeal as bravely as they did. 

"Mr. Mintry gave his recollection of the big earth- 



quake of I nesday (April 4y : It was a few mil 

aftei 12 o'clock. The men had already left the der- 
ricks. Suddenly there was a peculiar Swaying of the 
giound and an explosion which I can haidly de- 
SCribe. It was heaviei than any Mast I evei heard. I 
was on horseback, and the- horse was frightened 
badly. At fust I thought of a boiler, but Looking 
along the- San Fernando Range as far as I couli 
east and west, there was a blinding cloud of dust. It 
rose directly up hom the- top of the range and was 

thick. All around me dust lose fiom the hills in the 
neai vicinity and earth and boulders came tumbling 
down. The shoe k lasted between 10 and 15 seconds. 
I looked across the valley and saw the same thing in 
the Casta* [( Mills. I hat shock was the wont 

and it was accompanied hy a rumbling sound. The 
shocks since that lime have been smaller ones. They 
hive not affected the flow of oil. There was not the 
slightest distui banc e in any ol the wells. I have been 
here for 10 years as superintendent of the oil wells, 
and this is the- fust time there has been an earth- 
quake in this vie inity.' 

"At the head of the canyon and at Mintryville, 
which is nearly '1 miles below, the first shoe k played 
havoc with the crockery in nearly all the houses in 
both places, and a lot of milk pans full of milk, a 
quantity ol eggs, and the stove and nearly every 
loose article in one house were thrown in a jumble 
on the floor and mixed up with the ashes. 

"The schoolhouse had a large brick chimney, and 
after the shake there was not a whole brick left. An 
immense stone came tumbling down a mountainside 
and landed in among the pipelines and tanks below, 
smashing things generally. 

"Strange to say, not one of the many huge derricks, 
which are from 40 to 70 feet in height, was oxer- 
turned, although they swayed in alarming manner. 

"The motion in all the shocks was a swaying mo- 
tion, and the direction was from northwest to south- 
east. An old and strong adobe house on what is 
known as the middle Newhall ranch, northwest of 
Newhall, was shaken completely down by one of the 
temblors." 

These reports, assembled by Holden, call for fur- 
ther comment. The unreliability of times has been 
noted previously; the best time for the main shock 
is probably 11:40 a.m. That it was called a few min- 
utes after 12:00, following the work break at noon, 
at the rather isolated community of Mintryville, 
probably only means that the office clock was fast. 



Historical Seismicity of Earthquake Area 



Directions of apparent oscillation are noted at sev- 
eral points. These, as usual, are of doubtful signifi- 
cance. Indoors, such observations are affected by the 
oscillation of the structure itself. Outdoors, when re- 
liable, they usually refer to directions transverse to 
the line from point of observation to epicenter, and 
are probably due to waves of 5-type. 

Alternate spellings "Castac" and "Castaic" have 
long been in use; the latter is now preferred. 

There was probably only one really large shock; 
suggestions that following ones were nearly as strong 
are not very convincing. It is not unlikely that some 
of the aftershocks originated at very shallow depth, 
with correspondingly increased intensity near their 
epicenters. The concluding note which concerned a 
ranchhouse probably means that it was damaged in 
the main shock and failed gradually during the after- 
shock sequence to the point of final collapse. 

Mintryville was probably not near the principal 
epicenter. Equally strong shaking is indicated at New- 
hall and Saugus, with landslides visible at a dis- 
tance in the mountains, just as in 1971. The fact 
that oil derricks were not damaged, nor production 
affected, makes it unlikely that local shaking at Min- 
tryville was as intense or as strongly long period as 
were the maximum motions of the 1971 earthquake. 
It is interesting that some small aftershocks felt at 
Mintryville were not noticed at Newhall; this would 
suggest that the epicenters of these, at least, were 
near Mintryville. Probably there was faulting of con- 
siderable extent. 

Note that the shaking was called "slight" at Los 
Angeles. Except perhaps at Mojave, reports from dis- 
tant points generally indicate lower intensity than 
for the same localities in 1971, which supports the 
idea that the main shock of 1893 was of lower mag- 
nitude than that of 1971. 

1894 July 29. This appears to have been a consid- 
erable earthquake, but its center is uncertain. Shak- 
ing heavy enough to cause much excitement, but 
apparently just below the level of damage, was re- 
ported for Los Angeles, Pasadena, Santa Ana, San 
Bernardino, and Mojave, and the intensity was not 
much less at Santa Monica. 

1906 April 18. Magnitude 8.3. The third of the 
known great earthquakes of California, involving dis- 
placements along the San Andreas fault from the 
Humboldt-Mendocino region south past San Fran- 
cisco to near San Juan Bautista. The area of Los An- 
geles and San Fernando was near the limits of ordi- 



nary perceptibility to persons; as is common near the 
margin for large earthquakes, the principal 
sensations were those of slow swaying, accompanied 
by swinging of doors, suspended objects, etc. 

1916 October 22. Magnitude 6. The strongest ef- 
fects of this earthquake, barely reaching the damag- 
ing level, were in the vicinity of Tejon Pass; field in- 
vestigators attributed it to the San Andreas fault. 
No surface faulting was found. The source possibly 
might have been on one of the local faults north of 
the San Andreas fault in that area; minor shocks 
have been located there instrumentally, particularly 
in 1941-42. Perceptibility to persons extended to 
Los. Angeles. A number of aftershocks, some possibly 
from slightly different epicenters, were reported; a 
notable one occurred on November 1. 

1919 February 16. This shock also is attributed 
with some uncertainty to the San Andreas fault. An 
epicenter on the White Wolf fault near that of the 
major earthquake of 1952 would fit the data some- 
what better. Perceptible shaking again extended to 
the Los Angeles-San Fernando area. 

1920 June 21 . This minor shock damaged typically 
weak California masonry buildings in and near In- 
glewood. Perceptible shaking extended over a wide 
area, including most of the San Fernando Valley and 
Los Angeles. This earthquake led Stephen Taber to 
identify and name the active Inglewood fault. It has 
sometimes appeared in lists of large earthquakes, pre- 
sumably because the maximum intensity of about 
VIII on the Rossi-Forel Scale has been misread as a 
magnitude 8. A review of the scanty evidence indi- 
cates that the true magnitude was about 4.9. 

1925 June 29. Magnitude 6.3. Destructive at Santa 
Barbara; perceptible generally in the Los Angeles 
area. 

1926 February 18. Offshore? Fairly strong along 
the coast from Santa Barbara to Ventura, and nota- 
bly inland at Simi and Santa Susana. Slight at Santa 
Monica and at Los Angeles. 

1927 November 4. Magnitude 7.5. A major earth- 
quake off the coast west of Point Arguello. A small 
seismic sea wave reached the coast. The tracks of 
part of the coast route of the Southern Pacific Rail- 
road were distorted so that traffic was interrupted 
temporarily. At Lompoc, numerous chimneys were 
wrecked. Shaking was perceptible to persons in most 
of the Los Angeles area. 

1930 August 30. Seismograms written at Pasadena 
and auxiliary stations were used to locate the epicen- 



10 San Fernando Earthquake <>\ 1971 



ter of this shot k iii the northern pari ol Santa Mon- 
ica Bay. The magnitude was placed ai 5.2. Percepti 
Mr shaking extended ovei the whole metropolitan 
area. Scattered minoi damage occurred neai 1 1 ic- 
coast. Anomalously strong shaking and correspond 
in» damage occurred in the western s.m Fernando 
Valley, especially ai and neai Chatsworth and Ow- 
ensmouth (latei renamed Canoga Park). Oik- ol the 
two dams ai the Chatsworth Reservoii was damaged 
by settling and severe cracking. It was reconstructed 
thereafter, and the new dam passed through the 
earthquakes ol 1933, 1952, and 1971 without dam- 
age. 

Because earthquakes have originated in the Chats- 
worth area in latei years, the question lias been 
raised whether there might not have been an error 
in the placing ol the epicentei in Santa Monica Bay. 
The present writer undertook a careful remeasure- 
ment of the original seismograms, which confirmed 
the earlier determinations ol recorded times. Even in 
the light of better information on wave speeds and 
crustal structures now available, it appeared that no 
reasonable reinterpretation would allow an epicenter 
more than a lew miles north of that previously as- 
signed. An epicenter in the Chatsworth ana is defi- 
nitely in conflict with the data, particularly with the 
well-determined time of first recorded motion at La 
Jolla. 

Smaller earthcpiakes in later years have been lo- 
cated at epicenters in Santa Monica Hay near that 
found for the 1930 shock. For most of these, more 
stations with better instrumentation have been avail- 
able than in 1930. 

It is possible that the shock in Santa Monica Bay 
was followed within less than 1 minute by a smaller 
one centering in the Chatsworth area. Such a shock 
could not be detected on the seismograms, where it 
would be obscured by the preceding event. Faulting 
that extends at depth from under Santa Monica Bay 
northward would offer a possible explanation, but 
there is little other support for such a speculation. 

1931 April 7. This shock, magnitude 4, was felt 
sharply in the San Fernando Valley, but without 
damage. In view of the discussion on the earthquake 
of August 30, 1930, it is interesting that the epicen- 
ter was close to Chatsworth, near a known and 
mapped fault. Within limits of error, this epicenter 
is the same as that for February 8, 1964. 

1933 March 10. The Long Beach eartheptake, mag- 
nitude 6.3, was attributed to displacement on the In- 



glewood fault The instrumentally determi 
center, close to that ol a foreshock on the previous 
is offshore between Newport Beach and Hun- 
tington Beach. Epicenters ol aftershocks indicate 
faultii tided northwest to 'he vicinity ol I 

I'.' ic li .nid Signal Hill. 

I here was let ions clam • ma- 

sonry, ovei the whole ol the- Los Angeles basm in 
I .os Angeles and Orange Court tending into 

the- old central area ol LOS Angeles city. In tlie San 
Fernando Valley, damage was generally slight, in- 
cluding ijiicks out of chimneys here and there. At 
s.m Fernando, shaking was sufficient only to upset 

small objee ts. 

1952 July 21. The majoi Kern County earthquake 
was ol magnitude 7.6 to 7.7. It originated "n the 
White Wolf fault. I here was minoi damage in the 
I.os Angeles area, large in total amount, including 
interioi damage to business blew ks in Los Angeles 
and Long Beach. Much more damage occurred at 
Santa Barbara. Slides were precipitated heie and 
there ovei a large part ol southern California. Some 
ol these occtnied in the mountains north of San rcr- 
nando Valley. I he clam in Dry Canyon was cracked 
seriously. 

1952 August 22. The Bakersfield earthquake was 
ol magnitude 5.8. This was an aftershock of the July 
21 eartheptake, but with its epicenter much nearer to 
Bakersfield, where it caused more apparent damage 
than the main shock: some of this, however, was a 
cumulative effect on structures weakened in July. 
Shaking was perceptible in most of the I.os Angeles 
and San Fernando area, but with practically no dam- 
age. 

1952 August 23. Magnitude 5.0. Its epicenter was 
at 34 30' X.. US" 13' W., not far from Acton. This 
also was felt widely in the Los Angeles metropolitan 
area. Coming only a few hours after the Bakersfield 
earthquake, it aroused much public excitement, 
which was augmented by preliminary speculations 
that it had originated on the San Andreas fault — al- 
though instrumental recordings quickly showed that 
such was not the case. The above epicenter, within 
limits of accuracy, will fit a known fault mapped as 
branching from the San Andreas system. 

1954 January 12. The largest late aftershock of the 
Kern County series was also generally perceptible in 
the Los Angeles area. 

1956 February 7. Two shocks, at an interval of 43 
minutes, were ol magnitudes 4.2 and 4.6. The second 



Historical Seismicity of Earthquake Area 11 



one caused minor damage at Newhall and vicinity. 
The epicenter, as revised in 1965, was at 33° 33.3' N., 
118°37.4' W. This is north of Castaic, practically in 
Elizabeth Lake Canyon where slides occurred at the 
time. It is well outside the area of aftershock epicen- 
ters of the 1971 earthquake. 

1964 February 8. Magnitude 3.7. Felt generally in 
the San Fernando Valley. Its revised location was at 
34° 14' N., 1 18°35i/ 2 / W., near Chatsworth. The shock 
of April 29, 1931, can be referred to the same point. 

1964 August 30. Magnitude 4.0. Also, it was felt 
generally in the San Fernando Valley. Epicenter was 
near 34° 16' N., 118°27' W.; within the limits of ac- 
curacy, this will fit the Mission Hills thrust fault. 



1965 July 16. Magnitude 4. Noticed by many in 
the San Fernando Valley. Epicenter was at 34°39' N., 
118 31'W., east of Castaic. 

Epicenters for the numerous minor earthquakes 
located in the given area from 1934 to 1970 show a 
general scattering like that observed for almost any 
equivalent area in southern California. There is no 
alignment or clustering that would suggest signifi- 
cant activity on any of the known faults, including 
those of the San Fernando group which were in- 
volved in the 1971 earthquake. However, epicenters 
are notably lacking in the central parts of the San 
Fernando Valley, although they are normally numer- 
ous around its periphery. 



San Fernando Earthquake: 
Seismological Studies and Their 
Tectonic Implications 



CONTENTS 


Page 




13 


Abstract 


13 


Introduction 


14 


Seismolocic Environment 


15 


Hypocentral Locations 


17 


Magnitudes 


18 


Focal Mechanisms and Tectonic 




Interpretations 


20 


Acknowledgments 


20 


References 



Adapted from article prepared for publica- 
tion in California Division of Mines and 
Geology Bulletin 196, Ch. 14. Contribution 
No. 2124, Division of Geological and Plane- 
tary Sciences, California Institute of Tech- 
nology. 



CLARENCE R. ALLEN 

THOMAS C. HANKS 

JAMES H. WHITCOMB 

Seismological Laboratory 
California Institute of Technology 
Pasadena, Calif. 



ABSTRACT 

Improved hypocentral locations have been ob- 
tained for the San Fernando earthquake and its 
larger aftershocks through the use of data from port- 
able stations installed in and around the aftershock 
area subsequent to the main shock. The main shock, 
at 14:00:41.8 G.M.T. on February 9, 1971, is now- 
assigned a magnitude (Ml) of 6.4 and a location at 
34°24.7' N., 118°24.0' W., h = 8.4 km. Fifty-five 
aftershocks of magnitude 4.0 and greater had oc- 
curred through December 31, 1971. The lunate- 
shaped epicentral distribution of aftershocks is 
consistent with the idea of southward thrusting along 
a disc-shaped fault surface, and aftershock depths as 
well as aftershock focal mechanisms suggest that the 
thrust surface dips about 35° toward N.20°E. How- 
ever, a distinct linear alignment of left-lateral strike- 
slip aftershocks parallel to the motion direction near 
the west boundary of activity suggests that the fault 
surface has a steep flexure along this line, down- 
stepped to the west, and both the planar distribution 
of aftershocks and the local geology support this 
concept. 

INTRODUCTION 

The purpose of this paper is to describe the seis- 
mologic aspects of the San Fernando earthquake of 
February 9, 1971, and its aftershocks, and to inter- 
pret these earthquakes in terms of a tectonic model 
of the associated faulting. Several reports on these 
subjects were prepared by the authors within 3 
weeks following the earthquake (Allen et al. 1971, 
Hanks et al. 1971, Whitcomb 1971a, and California 
Institute of Technology 1971), and this paper up- 
dates these studies utilizing information recorded by 
the California Institute of Technology (C.I.T.) net- 
work through December 31, 1971. By this time, the 



13 



H 



San Fernando Earthquake <>j I'j7I 



principal aftershock activity seems to have con- 
cluded, although small aftershocks still continue. 
During the seismological investigations, particulai el 
fort has been made to gain an understanding ol the 
tec ton i( mechanism oi the earthquake the configu- 
ration of the fault surface, the Source mechanism of 
the main shock and aftershocks, and the tectonu en- 
vironment of (he faulted region. Preliminary conclu- 
sions on these topics ate summarized herein, al- 
though it should he recognized that studies are 
vigorously continuing and much detailed, substantiat- 
ing evidence as well as possible modifications will be 
presented in subsequent papers. 

SEISMOLOGIC ENVIRONMENT 

In the years before 1971, the San Fernando area 
was characterized by low to moderate seismic activity 
not unlike that of many other paits of southern Cali- 
fornia. Indeed, the 1934-63 strain-release maps 

(Allen et al. 1965) indicated that the northern San 
Fernando Valley was seismically less active than most 
other parts of the greater Los Angeles area. Nothing 
that has been recognized in the very recent seismic 
history seems to suggest that this area, more than any 
other area, was particularly likely to experience a 
magnitude 0.4 earthquake. It should be kept in 
mind, however, that an earthquake of at least this 
magnitude occurs somewhere in the southern Cali- 
fornia region on the average of about once every 4 
years (Allen et al. 196.5) , and in this sense the San 
Fernando earthquake was no great surprise. An 
earthquake of this same magnitude occurred in 1968 
in the Borrego Mountain area 220 km southeast of 
Los Angeles, but damage was small because — unlike 
the 1971 event — it occurred in a remote location. 

Between 1934 and 1971, which is the interval dur- 
ing which epicentral locations of southern California 
earthquakes have been listed by C.I.T., only about 
10 earthquakes of magnitude 3.0 and greater oc- 
curred in the area that corresponds to the epicen- 
tral region of the San Fernando earthquake (figs. 1 
and 2) . Before 1934, however, one earthquake is of 
special importance; this is the so-called Pico Canyon 
earthquake of 1893 (Tovvnley and Allen 1939), 
which was apparently centered only slightly west of 
the 1971 epicenter and was of only slightly lesser 
magnitude. It does indicate, significantly, that mod- 
erate earthquakes of this size were not unknown in 
the region. 



WSMA 







A 



B Q ■■ 



GOK 

A AIRC 



AGM 

▲ IND 



>/ >s 



LTU 

A 



lBLA 






MWC 

"Mo 










Figure I .— Aftershock area of S^ , i Fernando earthquake idottrd 
line), showing locations o] seismogiaph stations | triangles) that 
• used in epicentral locations of this stud-). Station data are 
I ii m table 1. 



Although most of the faults of the San Fernando 
area had not been generally recognized by geologists 
and seismologists as "active" prior to 1971, abundant 
unpublished evidence indicated that this was indeed 
the case. Particularly along the Tujunga segment of 
the San Fernando fault, geologists ol the Metropoli- 
tan Water District had — long before the earthquake 
— carefully documented the thrusting of older rocks 
over very young gravels (Proctor et al. 1972) along 
the same fault which broke on February 9. On the 
other hand, such evidence of geologically very recent 
displacements is becoming more and more wide- 
spread along many faults in coastal California, and 
there was no known reason to have picked out the 
San Fernando fault more than many of the others as 
being a particularly likely candidate for an earth- 
quake in 1971. The lesson is clear: Until we gain 
better geologic and seismologic understanding of the 
relative activity of various fault zones, all of coastal 
California must be considered to be one of relatively 
high earthquake hazard. 



Seism ological Studies and Their Tectonic Implications 15 




Figure 2. — Earthquakes <>j the San Fernando series, magnitude 4.0 
and greater through December 31, 1971. Solid circles represent 
"A" locations (see text), open circles "B" locations, and heairy Xs 
"C" locations. Doited line show, limits of most aftershock activity 
including many smaller shocks than those shown. Cross section 
A-A' is shown in figure 4. 



HYPOCENTRAL LOCATIONS 

In our earlier papers, Allen et al. (1971) summa- 
rized the seismological data of the first 3 weeks based 
only on the permanent stations of the C.I.T. net- 
work, while Hanks et al. (1971) located much more 
precisely a number of aftershocks during a particular 
18-hour period on the basis of C.I.T. portable sta- 
tions installed in the epicentral region within a few 
hours of the main shock. In this paper, we attempt 
to use data from the C.I.T. portable stations, in ad- 
dition to those of several other agencies (table 1 and 
fig. 1), to establish correction factors to make more 
effective use of the more distant permanent stations 
that were the only source of seismic information dur- 
ing the first few hours when the great bulk of after- 
shock activity occurred — as well as later in the after- 
shock sequence when most of the portable stations 
had been removed. For the purpose of presenting a 
homogeneous body of data, only shocks of magnitude 
4.0 and greater have been listed in table 2 and por- 
trayed in figure 2. We feel that this listing is rela- 
tively complete even within the first few minutes fol- 
lowing the main shock, for which we relied heavily 
on the low-gain (4x, lOOx) instruments of the Pasa- 
dena network as well as on the remarkable 6-min- 



Table 1 .—Seismographic stations whose data were used in epicentral locations shown in figure 2 and in table 2 



Station 



Agency 



Latitude 
North 



Longitude 
West 



Distance Period of 
operation 



AGM Agua Dulce EML 

BLA Blayney CIT 

BQR Bouquet Canyon CIT 

BRC Brown's Canyon CIT 

CSP* Cedar Springs DWR 

GOK Golden Oak Ranch CIT 

GSC* Goldstone CIT 

IND Indian Canyon CIT 

IRC Iron Canyon CIT 

ISA* Isabella CIT 

LTU Little Tujunga UCSD 

MLM Mill Creek Summit EML 

MWC Mount Wilson CIT 

OMM Oat Mountain EML 

PAS Pasadena CIT 

PLM* Palomar CIT 

PYR Pyramid DWR 

RTM Ritter Ranch EML 

RVR* Riverside CIT 

SBLG Laguna Peak USGS 

SOC Soledad Canyon CIT 

SUS White Oaks Park USGS 

SYP* Santa Ynez Peak CIT 

TRP Trippet Ranch USGS 

WSM Warm Springs EML 

* Asterisk indicates distant stations used only for locations of 

shocks during the first few hours before temporary stations were 
established. Agency designations are: CIT, California Institute of 
Technology; DWR, California Department of Water Resources; 



km 



34 29.5 1 


18 


19.3 


14.7 


2/10-4/24 


34 18.8 


18 


26.7 


20.6 


3/02-present 


34 33.5 


18 


25.5 


18.9 


2/09-5/07 


34 17.6 


18 


35.4 


23.5 


2/09-5/07 


34 17.9 


17 


21.5 


97.2 


Permanent 


34 23.1 


118 


28.3 


11.4 


2/10-5/06 


35 18.1 


16 


48.3 


176.1 


Permanent 


34 25.2 


118 


16.2 


15.2 


2 10-4/22 


34 23.3 


118 


23.9 


9.3 


2/09-5/07 


35 38.6 


,18 


28.6 


139.0 


Permanent 


34 17.7 


118 


21.6 


16.0 


2/09-2/11 


34 23.4 


118 


04.8 


31.2 


2/10-4/24 


34 13.4 


118 


03.5 


39.1 


Permanent 


34 19.8 


118 


36.0 


22.5 


2/25-4 22 


34 08.9 


118 


10.3 


37.0 


Permanent 


33 21.2 


116 


51.7 


184.5 


Permanent 


34 34.1 


118 


44.5 


37.1 


Permanent 


34 35.8 


118 


14.8 


26.7 


2/10-4/22 


33 59.6 


117 


22.5 


105.6 


Permanent 


34 06.6 


119 


03.9 


70.2 


Permanent 


34 26.1 


118 


21.7 


10.0 


2/10-5/06 


34 17.3 


118 


39.8 


29.0 


2/12-4/24 


34 31.6 


119 


58.7 


145.5 


Permanent 


34 05.4 


118 


35.1 


40.4 


2/12-4/24 


34 36.4 


118 


33.5 


27.6 


2/10^/24 



EML, Earthquake Mechanism Laboratory of NOAA; UCSD, 
University of California at San Diego; and USGS, National Center 
for Earthquake Research of U.S. Geological Survey. Distance is that 
to hypocenter of main shock. 



16 



San I'Ci nit mil) Earthquake of I'fil 



Table 2.—Shoctu »\ ion Fernanda teriei of magnitude 1.0 "»"/ graaten February * through Dewewbtt 11 W7J 





Date 1971 


1 jiii' 
GMT 


Latitude 

>rth 








■ 




1, 


m 


s 




o # 










2 09.. . 


14 


00 41 B 




118 24 


B 4 


B 


h 4 


2 09. . . 


14 


01 

01 

111 
III 
III 

01 
02 
02 
02 
02 
03 
03 
in 

Ml 

04 

(M 

m 
i)-. 
05 
i)7 
07 
07 
08 
08 
08 
08 

10 


08 














2 09. . . 


14 

14 

14 

14 

14 

14 


',; 










2 09. 


40 










4 1 


2 09. . 


r ,o 














2 09. . 


54 












4 2 


2-09.. . 












4 1 


2 09. . 


03 










4 1 


2 09. 


14 

11 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 

14 


30 










4 ■, 


2-09.. . 


51 










4 7 


2-09.. . 


44 












', a 


2-09.. . 


25 












4 4 


2 09. . . 


46 












4 1 


2 09 . 


07 












4.1 


2-09.. . 


34 












4 2 


2-09.. . 


39 












4 1 


2-09.. . 


44 












4 1 


2-09.. . 


40 












4.2 


2-09. . . 


41 












4 1 


2-09. . . 


50 












4.1 


2-09.. . 


10 












4 


2-09 . . . 


30 












4.0 


2-09.. . 


45 












4.5 


2-09. . . 


40 












4.0 


2-09... 


07 












4.2 


2-09.. . 


38 












4 5 


2-09. . . 


53 












4 6 


2-09.. . 


21.5 


34 


21.3 


118 19.0 


-2.0 


C 


4.7 


2-09.. . 


14 

14 


10 

16 


28 












5.3 


2-09... 


12.9 


34 


20.3 


118 19.9 


11.1 


C 


4.1 


2-09.. . 


14 


19 


50.4 


34 


21.4 


118 24.4 


11.8 


c 


4 


2-09. . . 


14 

14 


M 
39 


36 . 1 ... 












4.9 


2-09... 


17.7 


34 


20.9 


118 23.9 


7.0 


c 


4 


2-09... 


14 


40 


17.4 


34 


26.0 


118 23.9 


-2.0 


c 


4.1 


2-09.. . 


14 


43 


47.5 


34 


20.8 


118 28.9 


5.9 


c 


5.2 


2-09.. . 


15 


58 


20.9 


34 


22.5 


118 20.1 


9.0 


B 


4.8 


2-09.. . 


16 


19 


2h.', 


34 


27.4 


118 25.6 


-1.0 


C 


4.2 


2-10.. . 


03 


12 


12.0 


34 


22.2 


118 18.1 


0.8 


B 


4.0 


2-10... 


05 


06 


35 . 7 


34 


24.7 


118 19.8 


4.7 


B 


4.3 


2-10. . . 


05 


18 


07.2 


34 


25.5 


118 24.9 


5.8 


B 


4.5 


2-10... 


11 


11 


34.6 


34 


23.1 


118 27.3 


6.0 


B 


4.2 


2-10... 


13 


49 


53.7 


34 


23.9 


118 25.1 


9.7 


A 


4.3 


2-10. . . 


14 


35 


26.7 


34 


21.7 


118 29.2 


4.4 


A 


4.2 


2-10.. . 


17 


38 


55.1 


34 


23.8 


118 22.0 


6.2 


A 


4.2 


2-10.. . 


18 


54 41.7 


34 


26.7 


118 26.2 


8.1 


A 


4.2 


2-21... 


05 


50 


52.6 


34 


23.8 


118 26.3 


6.9 


A 


4.7 


2-21... 


07 


15 


11.8 


34 


23.5 


118 25.6 


7.2 


A 


4.5 


3-07... 


01 


33 


40.5 


34 


21.2 


118 27.4 


3.3 


A 


4.5 


3-25... 


22 


54 09.9 


34 


21.4 


118 28.5 


4.6 


A 


4.2 


3-30. . . 


08 


54 


43.3 


34 


17.7 


118 27.8 


2.6 


A 


4.1 


3-31... 


14 


52 


22.5 


34 


17.2 


118 30.9 


2.1 


A 


4.6 


4-01... 


15 


03 


03.8 


34 


24.7 


118 25.2 


7.1 


A 


4.2 


4-02.. . 


05 


40 


25.1 


34 


17.0 


118 31.7 


3.0 


A 


4.0 


4-15... 


11 


14 


32.0 


34 


15.9 


118 34.6 


4.2 


A 


4.2 


4-25... 


14 


18 


06.5 


34 


22.1 


118 18.9 


-2.0 


B 


4.0 


6-21... 


16 


01 


08.5 


34 


16.4 


118 31.9 


4.1 


B 


4.0 


Note: 


See text for explanation of Q (Quality). 



















ute-long accelerograph record from Pacoima Dam 
(Trifunac and Hudson 1971) . 

Twenty-two aftershocks of magnitude 3.5 and 
greater that were particularly well located by the 
portable stations were used to establish correction 
factors for the more distant permanent stations. In 
general, the portable stations that were used in- 
cluded most of the C.I.T. and Earthquake Mecha- 
nism Laboratory (EML) stations (table 1) as well 



as the three U.S. Geological Survey (USGS) indi- 
cated stations for a more limited number of shocks. 
Although the more distant stations of the C.I.T. net- 
work (those indicated by an asterisk in table 1) 
were not used in the precise locations, time residuals 
at these stations were calculated in each case, and the 
average traveltime correction factors thus obtained 
for these and the other permanent stations are as fol- 
lows: 



Seismological Studies and Their Tectonic Implications 17 



Station 


Seconds 


PAS 


+0.2 


MWC 


-.1 


PYR 


-.2 


SYP 


+ .6 


ISA 


+ .5 


GSC 


+ .2 


CSP 


+ .1 


PLM 


+ 1.3 



In addition, correction factors were applied to some 
of the portable stations in the southwestern part of 
the aftershock region, where considerable thicknesses 
of alluvium and sedimentary rocks are locally pres- 
ent as contrasted to the basement rocks that closely 
underlie most of the rest of the area. These correc- 
tion factors, based on the local geology, were: BLA, 
-0.5; BRC, -0.3; OMM, -0.3; SUS, -0.2; LTU, 
— 0.2 second. All of the above traveltime correction 
factors were applied to a computer location program 
based on the three-layer southern California crustal 
model of Press (1960) . In actuality, this model is 
clearly a gross oversimplification; in their explosion 
calibration of the USGS network in this same area, 
Wesson and Gibbs (1971) demonstrated that the 
local geology and crustal structure are very compli- 
cated and variable. 

One effect of using both the traveltime correction 
factors and the larger number of close-in stations has 
been to assign generally shallower hypocentral 
depths than those obtained earlier. Thus, for exam- 
ple, the hypocenter of the main shock is now as- 
signed a depth of 8.4 km (table 2) instead of the 
earlier 13.0 km (Allen et al. 1971), although the ef- 
fect on the location of the epicenter is less than 1 
km. 

Hypocenters obtained in this study have been di- 
vided into three categories of accuracy (table 2) , de- 
pending on the number and location of stations used 
in the solution and on the standard error of the com- 
puter solution. We feel that "A"-quality locations 
are generally accurate to within 2 km horizontally 
and 4 km vertically, "B"-quality hypocenters are felt 
to be accurate to within 4 km horizontally and 8 km 
vertically, and "C"-quality solutions are still less ac- 
curate. Those hypocentral locations in the vicinity of 
the main shock probably are much better than these 
standards, and the depths of the deeper shocks are 
more accurately determined than those of shallow 
focus. The figures represent somewhat subjective but 
conservative judgments based on attempts at location 
under a wide variety of assumptions as well as on the 



comparison of some of our solutions with the largely 
independent USGS solutions based on explosion cali- 
bration (Wesson 1971). 

Because of the difficulty in obtaining hypocentral 
solutions for the numerous large aftershocks that oc- 
curred within the first 10 minutes following the 
main shock (table 2) , it is dangerous to attempt to 
draw conclusions about possible migrations in after- 
shock activity with time. It nevertheless may be sig- 
nificant that all of the larger aftershocks that we 
have located in the southwestern extremity of the af- 
tershock zone — near Chatsworth and Granada Hills 
(fig. 2) — occurred relatively late in the aftershock 
period. The largest flurry of activity started almost 2 
months after the main shock and included the shal- 
low, magnitude 4.6 shock of March 31 that locally 
caused more damage in Granada Hills than did the 
main shock itself (Barrows et al. 1971 — reprinted in 
this volume) . 

MAGNITUDES 

The local magnitude (M L ) of the San Fernando 
earthquake main shock was tentatively given as 6.6 
by Allen et al. (1971) and by the California Insti- 
tute of Technology (1971) on the basis of initial ex- 
amination of the low-gain (4x) Wood-Anderson 
N-S seismogram written at Pasadena. Subsequently, 
other low-gain instrumental records of the Pasadena 
network have been examined in detail, and we 
herein update our original estimate of M L on the 
basis of records from Riverside, Cottonwood, and 
Santa Barbara, in addition to Pasadena. All normal- 
magnification (2800) Wood-Anderson instruments 
were off scale, such as those at Barrett and Tine- 
maha. Resulting magnitude assignments from the 
various low-gain instruments are as follows: 

Station Direction Magnifi- Ml 

cation 

Pasadena N-S 4x 6.7 

Riverside N-S 4x 6.5 

Santa Barbara E-W lOOx 6 . 3 

Cottonwood N-S lOOx 6.3 

Cottonwood E-W lOOx 6.3 

The Pasadena determination is subject to the addi- 
tional uncertainty that the — log A n correction (Rich- 
ter 1958) is a very sensitive function of distance 
for epicentral distances of less than 50 km. 

On the basis of these determinations, we assign 
M L = 6.4 to the San Fernando earthquake. This 
compares closely to the mean magnitude of 6.48 as- 



IK 



San Fernando Earthquake <>\ i'fll 



signed by Boll and Gopalakrishnan (1973) from 
four stations of the Berkeley network. The Prelimi 
nary Determination <>f Epicenters (PDE) listing by 
the National Earthquake Information Centei 
(NEIC) of NOAA is M s = 6.5, m b = 6.2, based on 
27!) stations repoi ting. 

Magnitudes have been assigned to aftershocks 
(table 2) on the basis ol readings from II standard 
Wood Anderson torsion seismometers at six widely 
spaced stations of the southern California network 
(Pasadena, Barrett, Cottonwood, Riverside, Santa 
Barbara, and Tinemaha) . Most magnitudes have 
been determined by averaging the readings from at 
least five of these stations. It is significant, however, 
that the average standard deviation for individual 
station readings foi 20 aftershocks ol magnitude 4.0 
and greater, each recorded at five or more stations, 
was 0.30. Considering this large variation observed 
on standard instruments in a wide variety ol azi- 
muths from the epicenter, some of the discrepancies 
between C.I.T. and Berkeley magnitudes reported by 
Bolt and Gopalakrishnan (1973) are not surprising. 

FOCAL MECHANISMS AND TECTONIC 
INTERPRETATIONS 

Fault-plane solutions for the main shock have 
been earried out independently by several investiga- 
tors (Canitez and Toksoz 1972, Dillinger and Espi- 
nosa 1971, Wesson et al. 1971, and Whitcomb 
1971a), and they agree that the basic mechanism of 
initial faulting was that of a thrust striking about 
N.70°W., dipping about 50° NE., and including a 
significant component of left-lateral slip in addition 
to the thrust component. This agrees remarkably 
well with the surface observations of faulting in the 
Sylmar-San Fernando area, some 13 km farther 
south. Kamb et al. (1971), for example, report the 
overall trend of the surficial fault break to be 
N.72°W., with north dips averaging about 42°; they 
also report "nearly equal amounts of north-south 
compression, vertical uplift (north-side up) , and 
left-lateral slip." 

The hypocentral locations of the main shock and 
aftershocks presented herein support the idea of dis- 
placement on a north-dipping thrust fault; and it 
seems particularly likely that the lunate-shaped dis- 
tribution of aftershock epicenters (figs. 2 and 3, 
Allen et al. 1971, Hanks et al. 1971, and Wesson et 
al. 1971) reflects the edge of the disc-shaped segment 













- 














■ ■ / 


'••. 






• 

■ A m 


•. 




/ 


# / 






• 


■• 


• • 






• 


• • / 




■ 
• • 


•*/ 


■••''' 


':.• 


,••" 


^A 





Figure 7. — Earthquakes of "A" and "B" hypocentral accuracy 
text) fot which good fault- plane solutions have been ob- 
tained, indicating eitlitr left-lateral strike slip on north-striking 
planes (squares) or thiusting on north-dipping planes (circles). 
A number of cpicentert are shown here that are not on figure 
2 because some earthquakes down to magnitude 3.0 hai'e been 
included. Dotted line is same as in figures 1 and 2. 



of the fault plane that slipped during the earth- 
quake, and where stresses remained high following 
the main shock. Very few aftershocks occurred in the 
vicinity of the surface break, presumably because 
stresses were completely relieved there. Two princi- 
pal areas of interest remain: (1) Aftershocks near 
Granada Hills and Chatsworth, at the southwest end 
of the aftershock zone (fig. 2) , are south of the pro- 
jected trace of the thrust fault and, therefore, do not 
fit so simple a picture of thrusting; and (2) focal- 
mechanism studies of aftershocks (Whitcomb 1971a 
and 1971b) include many shocks of strike-slip char- 
acter that demand an explanation more complicated 
than that of a simple thrust surface. 

Disregarding momentarily those aftershocks near 
Granada Hills and Chatsworth, it is clear from figure 
4 that the average dip of the zone of faulting north 
from the fault trace is considerably less than the 50° 
dip indicated by the focal mechanism of the main 
shock. One might explain this by systematic errors in 
the depth assignment of the hypocenters shown in 
figure 4, but substantiating evidence of the relatively 
shallow dip of the fault zone is given by the motion 



Seismological Studies and Their Tectonic Implications 19 



Surface 
fault trace 
t 



^ f~ 



• X 

5 



:v ■ 



X 



Figure 4. — Vertical cross section along line A- A' of figures 2 and 3, 
with hypocenters projected into plane of section. Symbols are 
same as in figure 3, except that additional small crosses indicate 
well-located earthquakes for which ambiguous or transitional 
fault-plane solutions have been obtained. 



vectors of individual focal-mechanism solutions. For 
some 65 aftershocks, the motion vectors closely con- 
centrate around an average plunge of 36° toward 
N.20°E., which corresponds closely to the dip of the 
hypothetical fault surface passing through the hypo- 
center of the main shock and the main concentration 
of aftershock hypocenters (fig. 4) . We prefer to be- 
lieve, therefore, that the steep dip of the fault plane 
portrayed by the focal mechanism of the main shock 
represents only the very initial motion, and that the 
fault displacement then propagated to the surface 
along a zone dipping some 15° less steeply. The fo- 
cal-mechanism data on which this and the following 
arguments are based will be presented in detail in a 
separate paper by Whitcomb (1973) ; the principal 
ideas have already been presented in Whitcomb 
1971a and 1971/;. 

It is clear from figure 3 that the aftershocks of 
dominantly strike-slip character delineate a relatively 
well-defined north-trending zone west of the epicen- 
ter of the main shock. If the solutions portrayed 
right-lateral slip, this zone might be visualized as a 
typical tear fault (Hills 1963) extending toward the 
ground surface, but their consistent portrayal of left- 
lateral slip demands instead that the thrust surface 
turn downward along this zone. These strike-slip 
earthquakes typically occur on fault surfaces dipping 
steeply westward, and we thus visualize a linear, 
steep flexure in the fault surface along this zone (fig. 
5) . Under this hypothesis, most of the strike-slip af- 
tershocks should be deeper than the thrust after- 
shocks to the east, and this is permitted but not de- 




>?P. T .-- ; -' 



Figure 5. — Schematic structural contour map showing simplified 
contours (in km) on fault plane and showing monoclinal flexure 
that might explain strike-slip aftershock mechanisms on steep 
west-dipping flank of flexure m fault surface. 



manded by the data of figure 4. It is significant, 
however, that all but one of the few thrust-type af- 
tershocks deeper than the main shock (fig. 4) occur 
within and west of the flexural zone, suggesting that 
the flexure is in essence a north-plunging, steep- 
flanked monocline that simply steps down the thrust 
plane to a somewhat greater depth west of the flex- 
ure, perhaps by 3 to 5 km. 

If indeed a flexure exists along the zone of strike- 
slip aftershocks, one geometric effect would be to dis- 
place the surface trace of the thrust fault to the 
south on the west side of the flexure (fig. 5) , and 
this may be the explanation of the aftershocks near 
Granada Hills and Chatsworth that are south of the 
trace of the fault as projected westward from the Syl- 
mar and Tujunga segments. Furthermore, their pre- 
dominant thrust-type focal mechanisms are consistent 
with their being west of the flexure, in analogy to 
those thrust-type aftershocks at the very northwest 
corner of the aftershock area (fig. 3) . It is also sig- 
nificant that all of the thrust-type aftershocks west of 
the flexure seem to have occurred well after the initi- 
ation of aftershock activity, on or after February 1 1 ; 
the larger shocks in the Chatsworth-Granada Hills 
area (fig. 2) all occurred after March 30 — very late 
in the aftershock period. 

Further support for the existence of a north-trend- 
ing flexure comes from the mapped geology of the 



20 San Fernando Earthquake of l'J7l 



area (Wentworth el al. 1971, fig. 2;. The trace ol 
the Santa Susana thrust, which lies parallel to and 
some 1 km north ol the San Fernando fault, makes a 
disiiiKi bend north ol Granada Hills in exactly tin- 
mannei postulated foi the San Fernando fault (fi^. 
5). Further, the faci thai basemenl rocks are widely 
exposed in the San Gabriel Mountains e.isi of tins 
/one, whereas only younger sedimentary ro< ks are ex- 
posed to the west, strongly supports the concept ol a 
flexinal downstep to the west in this area. 

Tims we argue thai the San Fernando earthquake 
was caused by displacemenl on a thrust fault- oi 
zone of thrust faults — dipping about 35°N. and strik- 
ing about N.7()"W. Particularly where the surface 
trace trended more westerly, as along the Syhnai a 
ineni, significant left-lateral slip occurred. A steep 
flexure in the thrust fault surface, parallel to (and 
probably controlling) the direction of slip and 
downsteppcd to the west, tended to limit the /one- ol 
initial breaking on the west and led to numerous af- 
tershocks of left-lateral strike-slip character on the 
steep west-dipping flank of the flexure. Some thrust 
displacements occurred later on the downstepped 
segment of the thrust fault west of the flexure, as in- 
dicated by aftershocks in the Chatsworth— Granada 
Hills area and in the northwestern extremity of the 
aftershock zone north of Solemint. Whitcomb (1971a 
and 1971/;) has pointed out that many of the after- 
shocks east of the main epicenter have fault-plane so- 
lutions which are consistent with normal faulting 
along steep northwest-trending faults; for simplicity, 
such shocks have not been shown in figures 3 and 4, 
but these events agree with the concept of congres- 
sional release resulting from a southward thrust to- 
ward the San Fernando Valley. 

ACKNOWLEDGMENTS 

Many agencies and persons supplied data from 
their portable stations that have been used in our 
study: Earthquake Mechanism Laboratory, NOAA 

(Don Tocher) ; National Center for Earthquake Re- 
search, USGS (Robert Wesson and Willy Lee) ; Uni- 
versity of California at San Diego (James Brune) ; 
and California Department of Water Resources 

(Paul Morrison) . At C.I.T., Gladys Engen, Mark 
Gaponoff, Jan Garmany, and John Nordquist read 
many of the records and carried out many of the 
computer solutions. This study was supported by the 



Caltech Earthquake Re i irch Affiliates and \>\ ih<- 
National Science Foundation (Gram GA29920). 

R] I ER1 N( I s 

Mien, Clan nee R Engei G.B Hani ["hoi ' Nord- 
quist I \( and rhatchei UK "Main Shod and I 
Vftershocks ol the s.m Fernando Earthquake Febru 
rhrougfi March I 1971," The San Fernanda Catifot 
Earthquake of February 9, 1971, Geological Sut < . P 
rional I'ajifi 733 t S Geological Survey and the National 
n i« .mil ttmospherie Administration, IS Department 
ol the Interioi and is Department of Commerce, Wash 
ington, I)f. 1971, pp. 17-20. 

\ll(ii. Clarence k St. Amand, Pierre, RJchter, Charles F., 
and Nordquist, | M "Relationship Between Seismicitj and 
Geologic Structure in the Southern California Region," 
Bulletin of the Seismological Society of America, Vol. 55, 
No 1. lug. 1965, pp " 

Barrows, \.C Kahlc | 1 Weber, F.H., Jr.. and Saul. R.B., 
Mn]> of Surface Breaks Resulting From the San Fernando. 
California, Earthquake of February 9, 1971, Preliminary Re- 
port II. Plate I. California Division of Mines and Geology, 
Sacramento, 1971, scale 1:24.000 

Bolt, B.A., and Gopalakrishnan, B.S.. "Magnitudes, After- 
shocks, and Fault Dynamics," California Division of Mines 
and Geology Bulletin 19fi. Ch. 15, Sacramento, 1973? (to be 
published) . 

California Institute of Technology. Division of Geological and 
Planetary Sciences. "Preliminary Seismological and Geo- 
logical Studies of the San Fernando. California, Earthquake 
of February 9. 1971," Bulletin of the Seismological Society 
of America, Vol. 61, No. 2. Apr. 1971, pp. 491-495. 

Canitez, Nezihi, and Tokso/ M. Nafi. "Static and Dynamic 
Study of Earthquake Source Mechanism: San Fernando 
Earthquake." Journal of Geophysical Research, Vol. 77, 
No. 14, May 10. 1972. pp. 2583-2594. 

Dillinger. \V '., and Espinosa. AT.. "Preliminary Fault-Plane 
Solution for the San Fernando Earthquake." The San Fer- 
nando, California, Earthquake of February 9, 1971, Geo- 
logical Survey Professional Paper 733. U.S. Geological Survey 
and the National Oceanic and Atmospheric Administration, 
U.S. Department of the Interior and U.S. Department of 
Commerce. Washington. D.C.. 1971, pp. 142-149. 

Hanks. Thomas C, Jordan. Thomas H.. and Minster. J. Ber- 
nard, "Precise Locations of Aftershocks of the San Fernando 
Earthquake 2300 (GMT) February 10-1700 February 11, 
1971." The San Fernando. California, Earthquake of Feb- 
ruary 9. 1971, Geological Survey Professional Paper 733. U.S. 
Geological Survey and the National Oceanic and Atmos- 
pheric Administration. U.S. Department of the Interior and 
U.S. Department of Commerce, Washington. D.C., 1971, 
pp. 21-23. 

Hills. E.S.. Elements of Structural Geology, John Wiley Re 
Sons, New York. N.Y., 1963, 483 pp. 

Kamb, Barclay, Silver, L.T.. Abrams, M.J., Carter, B.A.. Jor- 
dan, Thomas H., and Minster, J. Bernard. "Pattern of 



Seism ological Studies and Their Tectonic Implications 21 



Faulting and Nature of Fault Movement in the San Fer- 
nando Earthquake," The Sari Fernando, California, Earth- 
quake of February 9, 1971, Geological Survey Professional 
Paper 733, U.S. Geological Survey and the National Oceanic 
and Atmospheric Administration, U.S. Department of the 
Interior and U.S. Department of Commerce, Washington, 
D.C., 1971, pp. 41-54. 

Press, Frank, "Crustal Structure in the California-Nevada Re- 
gion," Journal of Geophysical Research, Vol. 65, No. 3, Mar. 
I960, pp. 1039-1051. 

Proctor, R.J., Crook, R., Jr., McKeown, M.H., and Moresco, 
R.L., "Relation of Known Faults to Surface Ruptures, 
1971 San Fernando Earthquake, Southern California." Geo- 
logical Society of America Bulletin, Vol. 83, No. 6, June 
1972, pp. 1601-1618. 

Richter, Charles F., Elementary Seismology, W.H. Freeman 
and Co., San Francisco, Calif., 1958, 768 pp. 

Townley, S.D., and Allen, M.W., "Descriptive Catalog of 
Earthquakes of the Pacific Coast of the United States, 1769 
to 1928," Bulletin of the Seismological Society of America, 
Vol. 29, No. 1, Jan. 1939, 297 pp. 

Trifunac, Mihailo D., and Hudson, Donald E., "Analysis of 
the Pacoima Dam Accelerogram — San Fernando, California, 
Earthquake of 1971," Bulletin of the Seismological Society 
of America, Vol. 61, No. 5, Oct. 1971, pp. 1393-1411. 

Wentworth, Carl M., Yerkes, R.F., and Allen, Clarence R., 
"Geologic Setting and Activity of Faults in the San Fer- 
nando Area, California," The San Fernando, California, 
Earthquake of February 9, 1971, Geological Survey Profes- 
sional Paper 733, U.S. Geological Survey and the National 



Oceanic and Atmospheric Administration, U.S. Department 
of the Interior and U.S. Department of Commerce, Wash- 
ington, D.C., 1971, pp. 6-16. 

Wesson, Robert L. (U.S. Geological Survey, Menlo Park, 
Calif.) 1971 (personal communication) . 

Wesson, Robert L., and Gibbs, J.F., "Crustal Structure in the 
Vicinity of the San Fernando, California, Earthquake of 
9 February 1971" (abstract), Transactions of the American 
Geophysical Union, Vol. 52, No. 11, Nov. 1971, p. 864. 

Wesson, Robert L., Lee, W.H.K., and Gibbs, J.F., "Aftershocks 
of the Earthquake," The San Fernando, California, Earth- 
quake of February 9, 1971, Geological Survey Professional 
Paper 733, U.S. Geological Survey and the National Oceanic 
and Atmospheric Administration, U.S. Department of the 
Interior and U.S. Department of Commerce, Washington, 
DC, 1971, pp. 24-29. 

Whitcomb, James H., "Fault-Plane Solutions of the February 
9, 1971, San Fernando Earthquake and Some Aftershocks," 
The San Fernando, California, Earthquake of February 9, 
1971, Geological Survey Professional Paper 733, U.S. Geo- 
logical Survey and the National Oceanic and Atmospheric 
Administration, U.S. Department of the Interior and U.S. 
Department of Commerce, Washington, D.C., 1971a, pp. 
30-32. 

Whitcomb, James H., "Focal Mechanisms of the San Fernando 
Aftershock Series" (abstract) , Transactions of the American 
Geophysical Union, Vol. 52, No. 11, Nov. 19716, pp. 862-863. 

Whitcomb, J.H., "The 1971 San Fernando Earthquake Series 
Focal Mechanisms and Tectonics," Reviews of Geophysics, 
in press, 1973. 



Felt Area and Intensity of 
San Fernando Earthquake 



CONTENTS 

Page 

23 Introduction 

26 Intensity ix-xi 

26 San Fernando, Sylmar, and Environs 

26 Summary of Faulting and Other 

Ground Effects 

2" Highways and Roads 

27 Dams 

28 Utilities 

2!' Buildings and Dwellings 

34 Intensity viii 

34 Granada Hills 

35 Mission Hills 

36 Newhall-Valencia Area 

36 Newhall 

37 Valencia 

37 Saugus and Soledad Canyon Areas 

38 Intensity vii 
47 References 



NINA H. SCOTT 

Seismological Field Stirvey 

Earth Sciences Laboratories 

Environmental Research Laboratories, NOAA 



INTRODUCTION 

Even though this earthquake was only of moderate 
magnitude (6.4) , it devastated buildings and dwell- 
ings; major highways; dams, underground gas, water, 
and sewer systems; and electrical facilities and equip- 
ment. With damage losses estimated at over $500 
million, it ranks as one of the major destructive 
shocks of the United States. 

Although 58 persons were killed and over 2,000 
were injured, clearly the time of occurrence 
(0(3:00:41.6 Pacific Standard Time) and the brief 
duration of strong shaking (about 10 seconds) were 
extremely fortunate circumstances for a great many 
other persons, as attested to by the collapsed freeway 
overpasses, the collapsed or partially collapsed com- 
mercial and industrial buildings, and the nearly de- 
molished Van Norman Dam. 

The epicenter was located at latitude 34°24.7' N. 
and longitude 1 18°24.0' W., about 8.7 miles north- 
northeast of San Fernando, in the San Gabriel 
Mountains south of Soledad Canyon; but the full 
impact of the shock's explosivelike force was felt in 
the San Fernando-Sylmar area. 

A very violent vertical motion was reported by 
some observers in the strongly shaken area, but, in 
general, observers reported the direction of motion 
as either north-south or east-west. 

The "generally felt" area was approximately 
80,000 square miles, but there were a few isolated in- 
stances of the shock being felt beyond this area: 
Bridgeport, Stockton, and Yosemite National Park, 
Calif.; Tonopah, Nev.; and Beryl, Utah (fig. 1) . 
The felt area was determined primarily from almost 
2,000 reports received through the earthquake ques- 
tionnaire card canvass conducted by the Seismologi- 
cal Field Survey. 

Intensities ranging from VIII-XI (fig. 2) oc- 
curred over approximately 190 square miles. A 
maximum intensity of XI was assigned to the Olive 
View Hospital in northern Sylmar area where por- 



23 



1M San Fernando Earthquake of I'Jl 1 




Felt Area and Intensity of Earthquake 25 




F .JRTER 
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AREA 





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NOICATES INTENSITY 



EPICENTRAL AREA 
SAN FERNANDO EARTHQUAKE 
FEBRUARY 9, 1971 



n I-* I.i E3 B" 



SCALE IN MILES 



Figure 2. — Epicentral area of San Fernando, Calif., earthquake of February 9, 1911. 



'ZU San Fernando Earthquake of l')li 

lions of new, reinforced concrete, earthquake-resis- 
tive buildings collapsed. Intensities ol IX X gener- 
ally were indicated in the Sylmai San Fernando area 
where ground disturbances were varied and wide- 
spread (Assuring, sliding, slumping, and compres 
sion-ridging) ; freeway overpasses collapsed, support 
ing piers sustained great damage, and many othei 
bridges were seriously damaged; two old earthhll 
dams were damaged and musi be rebuilt, with one 
on the verge ol collapse; underground gas, sewer, 
and watei pipelines wen- completely out ol service in 
some areas as the result of the great number ol 
breaks; railroad tracks bent; electrical facilities were 
greatly damaged; unreinforced concrete buildings 
collapsed; and reinforced concrete buildings were se- 
riously damaged. Buildings ol all types commercial, 
industrial, and dwellings were damaged exten- 
sively. Many were beyond repair and condemned. 

In the intensity VII /one, considerable damage oc- 
curred, but mainly to older buildings and dwellings. 
Some were posted as "unsafe," and others reportedly 
will be demolished, notably in the Alhambra, Bev- 
erly Hills, Burbank, and Glendale areas. It was re- 
ported that a few large buildings sustained some 
structural damage, but damage to large or high-rise 
buildings generally was minor— cracked partitions, 
fallen plaster, and broken windows. There were nu- 
merous reports ol inoperative elevators. Thousands of 
chimneys were damaged. 

All intensities in the sections that follow are rated 
according to the Modified Mercalli Intensity Scale of 
19.'51 (Wood and Neumann 1931). Descriptions for 
intensity VI and below are not included in this 
paper. 

The following fatality, injury, and damage figures 
were taken from Los Angeles County Earthquake 
Commission (1971) : Relative to the four persons 
killed at other locations, it was reported by the press 
that a woman was killed by the collapse of her home 
at 136 e >6 Borden Avenue in Sylmar; one child was 
killed by the collapse of a commercial building at 
1113 First Street in San Fernando; and a man was 
killed by collapse of an old building (Mission Inn) 
in downtown Los Angeles. It is not known at this 
time just where the other fatality occurred. 

Fatalities: 

Olive View Hospital 3 

Veterans Administration Hospital 49 

Collapse of freeway overpass 2 

Other 4 



"Reports of fatalities have varied and are quot 
frequently as 64. I Ik-sc- figui pro- 

vided by the Medical Examinei Coronet J he-\ in 

c hide onh those \\ ho died as a ehiee t e onsequei, 
the- earthquake I Ley do not include fatalities from 
heart attack occurring coincident with the earth- 
quake oi accidents while- being transported from the 

SC CMC." 

An estimated 2,400 were injured. 

Damage: Structures posted as unsafe, 1 489; clam- 
aged, 30,684, including mobile homes Riesc fig- 
ures represent damaged dwellings, apartment build- 
ings, c oinineic lal, industi ial, en , 

"Some- additional structures were |>osled unsafe- in 
jinisdie tieins othei than the c ities e>| I .os Angeles and 
San Fernando and the counts of I .os Angeles 
of the damage in these othei jurisdictions was to 
pre-1933 bi ic k structures and chimneys. Hundreds of 
the latin were damaged. 

"I he- damage inflicted by the earthquake has been 
estimated to be ovei S">00 million, and it has been 
reported that approximate!) B50 homes, 05 apart- 
ment buildings, and 574 cemimercial-industrial 
buildings were so damaged that they were vacated; 
some 4,800 homes. 265 apartment buildings, and 
1,125 commercial buildings had appreciable damage; 
and about 30,000 struc tures had lesser damage. It 
was reported that about 1,700 mobile homes were 
damaged substantially in the earthquake area." 

Damage estimates: 

Jurisdiction or agency Public Private 

property property 

City of Los Angeles $92,000,000 5210,000,000 

County of Los Angeles 100,000,000 6,800,000 

Other local jurisdictions 5,200,000 30,000,000 

State of California 15,000,000 

Federal Government 10,000,000 

Metropolitan Water District 6,000,000 

General Telephone 4, 700,000 

Los Angeles School District 22,500,000 

Southern California Gas Company 2,000,000 

Southern California Edison 

Company 750,000 



Total 5250,700,000 5254,250,000 

Total (public and private). 5504,950,000 

INTENSITY IX-XI 

San Fernando, Sylmar, and Environs 

Summary of Faulting and Other Ground Effects 

The earthquake created a zone of discontinuous 
surface faulting that extended from the Bee Canyon 



Felt Area and Intensity of Earthquake 27 



area (west of Upper Van Norman Lake) roughly 
eastward across the Sylmar-San Fernando area to 
the Big Tujunga Canyon area north of Sunland. 
The main rupture segment, designated the Sylmar 
segment, extended eastward from the intersection of 
Hubbard Street and Glenoaks Boulevard in the 
southern Sylmar-northern San Fernando area, across 
Foothill Boulevard, to the Foothill Nursing; Home. 
Although it was in this segment that the greatest and 
most complex ground distortion and concentration 
of damage occurred, prominent ground displace- 
ments, fractures, and scarps were observed in other 
segments of the fault zone, notably in the Tujunga 
segment that extended from the vicinity of the Foot- 
hill Nursing Home eastward into Big Tujunga Can- 
yon, and in the area north and northwest of Upper 
Van Norman Lake. Surface faulting also occurred in 
areas away from the main zones of faulting, includ- 
ing an area just east of the Veterans Hospital; in the 
Lopez and Kagel Canyon areas; on Kagel Mountain 
(just east of Pacoima Reservoir) ; and in areas east 
of Lower Van Norman Lake along the Golden State 
Freeway. Landsliding and severe ground fractures 
were responsible for extensive damage in areas not 
associated with faulting. There was severe ground 
cracking in the Olive View Hospital area, in the 
southwestern Sylmar and San Fernando areas, in the 
upper Granada Hills area west of Van Norman 
Lakes, and in many areas north and east of the Syl- 
mar-San Fernando area. There was extensive land- 
sliding and slumping, along with numerous fissures 
and sand boils, in the Van Norman Lakes area. It 
was reported that the appearance of the sand boils 
indicated liquefaction of soil in this area. The most 
damaging slide (the Juvenile Hall slide) occurred 
in the Upper Van Norman Lake area, where prac- 
tically all structures and facilities located in or cross- 
ing this slide were damaged very severely — highway 
overpasses and bridges, railroad lines, pipelines, and 
canals; Sylmar Converter Station; San Fernando 
Valley Juvenile Hall; Joseph Jensen Filtration Plant; 
and other structures and facilities. Landslides and 
rockfalls were widespread and numerous, with high 
concentrations in the foothills and mountainous 
areas. Massive rocks fell in the Pacoima Dam area. 
Many roads were blocked by landslides and rockfalls. 
One of the larger slides, approximately 600 feet wide, 
occurred on the east side of Schwartz Canyon. The 
violent, vertical motion of this earthquake also was 
evident in the observance of widespread and numer- 



ous shattered ridgetops, with the soil of previously 
smooth surfaces upthrown, overturned, and pulver- 
ized. This type of ground rupture was especially 
exemplified west of Grapevine Canyon, in the hills 
north of the Olive View Hospital, near Wallaby and 
Rajah Streets in the northeasternmost corner of 
Sylmar, west of Balboa Boulevard, east of Bartholo- 
maus Canyon, and on the ridges above Oliver and 
Schwartz Canyons. 

Highways and Roads 

Most of the major and spectacular damage to high- 
way structures and bridges occurred in an area along 
U.S. Highway 5 at the interchanges of Routes 5/210 
and 5/14, located about 1 mile apart. At the Route 
5/210 interchange (Foothill Boulevard and Golden 
State Freeway) , three highway overpasses totally col- 
lapsed and two required rebuilding. Two men were 
killed at this location when one of the overpasses col- 
lapsed onto their truck. Bridge columns failed. At 
the Route 5/14 interchange (Golden State Freeway 
and Antelope Valley Freeway) , two spans of a nine- 
span bridge collapsed. A bridge also collapsed at the 
interchange between the Golden State Freeway and 
San Diego Freeway. It was reported that almost all 
remaining structures in the general vicinity of the 
interchanges (possibly as many as 70) were damaged 
to some extent, many requiring extensive repair. 
Bridges on the Antelope Valley, Foothill, and San 
Diego Freeways also were damaged seriously, espe- 
cially along Foothill Freeway in the Sylmar-San Fer- 
nando area. The press reported that the Newhall 
and Old Sierra Highways and Bouquet Canyon 
Road were closed by slides and bridge damage. 
There was some bridge damage along the Soledad 
Canyon Road areas east of Saugus. Many other roads 
were blocked by slides in the San Gabriel Moun- 
tains. Numerous roads and city streets in northern 
San Fernando Valley were made dangerous or im- 
passable by landslides, cracks, and upheaval. Rail- 
road traffic also was disrupted because of displace- 
ment and distortion of rails and a collapsed overpass 
that fell on the tracks. In front of the Juvenile Hall 
facilities, railroad tracks were twisted, broken, and 
displaced as much as 52 inches. 

Dams 

The old Upper and Lower Van Norman earthfill 
dams were damaged and require rebuilding. The 



2K 



San Fernando Earthquake of J971 



Lowei Dam was so (lose to complete failure thai ap- 
proximately no, ooo persons wen- evacuated lor sev- 
eral days from the endangered areas below the dam. 
The reservoii keepei ol Lowei Van Norman R 
voir reported the following: "We live on the reser- 
voir grounds .11 the- bottom ol the- dam on the wesi 
end (1 1729 Strandwood Avenue) . No ground cracks 
around house. Chimney badly damaged; one crack in 
foundation. Stove, refrigerator, and dressei shifted. 
No broken plaster; no broken windows. Damage 
slight. My wife and child were up, getting ready lor 
school. She heard the shock coming. I was asleep. I 
tried to get out of bed but couldn't, until the- worst 
of it was over. I made a c|nic k check on the- family 
and a quick check ol the house, then cliessed and 
went to check the dam. When I got to the- main toad 
going to the lop of the clam, I could see through the 
dust an irregularity of the crest ol the structure 
below, looking to the top. I drove to the- top ol the 
dam and around the west abutment and saw the 
damage to the face. It was hard to believe what I 
saw." 

It was reported the Pacoima Dum, located about 
1 1/4 miles northeast of the San Fernando Veterans 
Hospital, sustained $1.5 million damage to its abut- 
ments. Massive rockslides blocked access roads to the 
dam. Waterlines were damaged. In view of the ap- 
parent high intensity in this area, the following, as 
reported by the caretaker of the dam, is of interest: 
"Caretaker's house is a one-story wood frame build- 
ing (built in 1953) , situated on loose fill (fill done 
in 1938) . It is approximately 40 by 40 feet and rests 
2 feet off the ground on a concrete perimeter foun- 
dation with wood plate around the foundation. 
There was no damage to the concrete foundation 
and only minor damage to the wood support. The 
brick chimney was undamaged. There were hairline 
cracks in ceiling plaster and above doors; no doors 
were out of plumb. Doors on a 6-foot-high hutch 
opened and the first row of glasses was thrown out; 
then the doors closed and rest of glasses did not 
break. Some objects fell in the house. Huge rock 
rolled down and broke outside stucco but the rock 
did not come through into the house. An old nearby 
house (built in 1937) had outside brick chimney 
separate from frame but the chimney did not fall. At 
the dam, an empty tank (under construction) 
shifted only about 6 inches off foundation." It was 
reported that Lopez and Hansen Dams sustained 
only minor damage. 



Utilities 

There was extensive and severe damage- to am 
giound waterlines, gaslines, vucis, tunnels, Hood 

control facilities, and e-le-etneal and powei facilities 

and Structures, It was reported that it will be- ii(-(c-s 

sary to completely rebuild the- sc-uc-r s\st<m m the 
area bounded by Hubbard Sue-e-i, Cienoaks lioule- 
vaid, Harding Street, and Eighth Stre-e-t. In the 
Uppei V.iii Norman Lake ana sections of several 
canals were badly damaged; se-wral flood control 
dikes suffered slumping. Reportedly, approximately 
million damage was done- to the- I .os Armeies 
Mood control lacilitie-s, and about one-half of this loss 
resulted from breakage- ol reinforced concrete open 
( hannels and underground box < hannels. In one case, 
breakage- extended for the length e>f a city blexk. 
Substantial damage- occurred to Wilson Canyon 
Channel, Mansfield Avenue Storm Drain, Pacoima 
Wash, I.opcv Canyon Channel, and (denoaks Boule- 
vard Drain, all in the San 1 e r nando-Sylmar area. 
Lopez Debris Basin, north of Hansen Dam, was seri- 
ously damaged. Damage was estimated at $0 million 
to the- Metropolitan Water District of Southern Cali- 
fornia facilities. At the Joseph Jensen Filtration Plant 
(about I, mile noithwcst ol Uppei Van Norman 
Lake), there was extensive ground cracking in the 
plant area, with lateral movement cjf 1 foot or more 
at the plant site. The Balboa Inlet Tunnel (14 ft in 
diameter) had about 300 feet of lining badly dam- 
aged at a point about 1,500 feet in from its down- 
stream portal. It was reported the San Fernando 
Tunnel (18 ft in diameter, 29,000 ft long, and ex- 
tending from Magazine Canyon to Pacoima Wash) 
experienced a 6i/£-foot vertical displacement between 
its portal and a point 4\/ 2 miles into the tunnel. The 
First and Second Owens River Aqueducts were dam- 
aged. The Second Aqueduct was damaged in its Sau- 
gus pipeline portion (pipes, buckled and supports 
moved) between Terminal Hill and Magazine Can- 
yon. Water service to the Granada Hills. Porter 
Ranch, Sylmar, and other high-elevation areas in the 
San Fernando Valley Avas disrupted by the many 
trunk] ine breaks on the Susana, Granada, and Ma- 
clay trunklines. On the Granada line, most of the 10 
or 12 breaks were in the Joseph Jensen Filtration 
Plant area. The wood roof collapsed at the small Ma- 
clay Reservoir on the Maclay High Line, and crack- 
ing occurred at the sides and corners of the basin. 
Damage at the Syhnar Converter Station (Pacific In- 
ter tie), just west of Upper Van Norman Lake, was es- 



Felt Area and Intensity of Earthquake 



29 



timated at approximately S22 million. It was re- 
ported that the most severe damage to this plant 
involved electrical equipment and underground con- 
duits. Such equipment as converters, transformers, 
and circuit breakers were damaged extensively. 
Heavy outdoor electrical equipment, some weighing 
many tons, was overturned. Many cracks, separations 
of concrete walls, and other building damage were 
noted. It was estimated that this facility would be 
out of operation for about 1 year. A power-generat- 
ing plant, north of the station, was also seriously 
damaged. There was severe damage to electrical 
equipment at the Olive Switching Station, about 
one-half mile west of the Sylmar Converter Station, 
where insulator-supported equipment collapsed and 
several large transformers overturned. Severe damage 
was sustained at the Olive View Power plant where 
large boilers were shifted as much as 4 feet and 
where tanks and motors were torn loose from an- 
chorages. Many elevated water tanks were damaged; 
some were shifted, overturned, and destroyed. A 
large steel tank, just north of Olive View Hospital, 
was ruptured. An elevated water tank, east of San 
Fernando Ranger Station in Lopez Canyon, was 
shifted from its pad and destroved. A Fiberglas tank, 
near the northwest shore of Lower J'an Norman 
Lake, shattered when it hit the ground. A large tank 
at Granada Hills was damaged. Many water wells 
were damaged. In general, all utility facilities — gas, 
electrical, and water — in the severely damaged areas 
of San Fernando and Sylmar were out of service. It 
was reported the water distribution system for the 
city of San Fernando was almost completely de- 
stroyed by ground cracking and violent shaking. All 
reservoirs leaked; two could not be repaired. Many 
underground gaslines and waterlines were separated, 
buckled, or fractured. Nearly every pipeline in the 
major ground-rupture zone was damaged. All tele- 
phone equipment in the Sylmar Central Office of the 
General Telephone Company (Polk Street and Bor- 
den Avenue) was totally destroyed. Damage to the 
building and equipment was estimated at S4.5 mil- 
lion. In the Sylmar area, many pole transformers were 
thrown down; insulators and crossarms were broken: 
wires and poles were knocked down; and cable was 
sheared off in underground ducts. Four gas transmis- 
sion lines, ranging in diameter from 12 to 26 inches, 
were damaged between Newhall and San Fernando, 
resulting in loss of gas supply to the San Fernando- 
Sylmar area. A main feeder gasline (16 in. in diame- 



ter) broke and erupted in flames on Glenoaks Boule- 
vard between Hubbard and Bledsoe Streets, shutting 
off service to 20,000 homes. Oilfield facilities and 
related structures sustained minor damage to tanks, 
roads, pipelines, and a few wells in Aliso Canyon, 
Cascade, Castaic, Xewhall. X ewhall-Potrero , Oak 
Canyon, Placerita, and Ramona oilfields. 

Buildings and Dwellings 

Olive View Hospital. — Major collapses of newly 
built reinforced concrete buildings occurred and oth- 
ers were seriously damaged. The second story of a 
two-story building dropped to ground level. Four 
five-story wings pulled away from the main building; 
three were toppled. This damage was reported to 
have been the result of severe ground shaking, not 
faulting. Three deaths occurred at this facility, one 
from falling debris and two when power was cut off 
from medical equipment. Ground and paving cracks 
and compression ridging were noted at the site. 

San Fernando Veterans Administration Hospital. — 
Major collapses of older unreinforced masonry build- 
ing occurred at this facility. Forty-nine were killed; 
many were injured. 

Holy Cross Hospital. — This seven-story reinforced 
concrete building sustained major structural damage. 
Extensive and severe cracking caused the building to 
be evacuated. Also, the nearby Indian Hills Medical 
Center building was badly damaged. 

Pacoima Memorial Lutheran Hospital (about ly 4 
miles southeast of Foothill Nursing Home) . — Major 
structural damage to a four-story reinforced concrete 
building occurred, causing it to be evacuated. 

San Fernando Juvenile Hall buildings. — There was 
severe and extensive damage to practically all build- 
ings; some collapsed. Fissures 18 to 24 inches wide 
and 4 to 5 feet deep were noted at the site. The 
buildings were evacuated. 

San Fernando Industrial Tract (east of the intersec- 
tion of Foothill Boulevard and Arroyo Street) . — Ma- 
jority of structures were posted as unsafe. Severe 
ground cracking, lurching, and compression ridging 
occurred. Sidewalks were torn up and buckled. 

Sylmar Industrial Tract (east of San Fernando 
Road in Bledsoe and Bradley areas) . — Majority of 
buildings were posted as unsafe. Many roofs and 
walls collapsed. Considerable ground cracking and 
compression ridging occurred. 



.'50 



San Fernando Earthquake <>\ 1971 



Foothill Nursing Home ('just east ol Foothill 
Boulevard and about i/g mile south ol San Fernanda 
Ranger Station) . I he building, ;i one story coru rete 
hlo( k structure, was severely damaged, I he curb and 
sidewalk in front of the building were raised about 3 
feel by surface faulting that also passed undei the 
building. 

School buildings. "Most schools in the San Fer- 
nando Valley were post-1933, and these experienced 
little damage from shaking. Some wood frame build- 
ings were shifted on their foundations, and some 
cracking was experienced. The foundations of sev- 
eral school buildings, such as Van Gogh Street Ele- 
mentary School and Sylmar High School, were dis 
rupted by permanent ground displacements, but 

Structural damage was not such as to constitute an 
undue hazard to occupants. However, in some cases. 
light fixtures and ceilings supposedly designed to 
withstand earthquake shaking fell, and these woidd 
have been hazardous. The generally good behavior 
of the school buildings in the San Fernando Valley 
is due mainly to the fact that they were well- 
constructed one- and two-story structures, mostly 
wood frame and plaster, that were significantly 
stronger than the minimum requirements of the 
building code. Of the pre-1933 schools, Morningside 
School at Maclay Avenue and Fifth Street in San 
Fernando was closest to the center of the earth- 
quake. One of the two structures at this site was a 
good quality, two-story brick bearing-wall building 
(1928) which was very badly cracked by the ground 
shaking. Although it would not have injured occu- 
pants during the earthquake, it did appear after- 
wards to be in a most dangerous condition, and it 
has been demolished. Since the earthquake, most of 
the old buildings have been closed. A few were 
judged to be in a good condition and not unduly 
hazardous to the occupants, and these will be used 
for a limited period of time." 

Dwellings. — Severe and extensive residential dam- 
age occurred in the area of permanent ground dis- 
placement, beginning in the area of Cdenoaks 
Boulevard and Hubbard Street and extending: east- 
ward across northern San Fernando (north of Maclay 
Avenue) into the foothills to the east. Many houses, 
including mobile homes, were very badly cracked and 
shifted from foundations. Many one- and two-story 
apartment buildings were also extensively damaged. 
Another area of severe, extensive damage to residential 



houses was between the Olive View Hospital rod the 
Veterans Administration Hospital where som< 
dences were damaged beyond repais rod some 

in stale- of collapse, where man\ ho .fled 

off foundations, and where practically all eoj. 

block walls and chimneys fell. Abo, mans dwellings 

in \ai ions stages ol c oust! uc tioii in an area east of the 

Veterans Administration Hospital were heavilj dam- 
aged, and some- c ollapsed. 

The majority ot the following rep'jrts were ob- 
tained through the questionnaire <ard camass eon- 
ducted by the- Seismologk a] Field Sur\< 

San Fernando: 

2043 Phillippi Street (about l*/ 4 miles southeast 
ol Olive Vie-w Hospital). "No one sound could be 
distinguished. The building and everything in it 

shook so violent!) that the combined sounds were 
deafening. In m\ block, streets split and were dis- 
placed in about 10 places; one place in street was 
buckled. Other streets in the area were split, cracked, 
twisted, and bu< kled far worse than my street. My 
chimney top shot straight up. then fell e>n roof. It 
was pulled straight up, with its reinforcement rods 
left in main body of chimney, and pulled a segment 
of the inside tile out of the main body of chimney. 
Swimming pools in area lost 5,000 gallons or more of 
water. One pool, two blocks away, was pushed under 
decking nearly to the house foundation. Water in 
toilet tank splashed all over the bathroom. Every sur- 
face in house was cleared of contents. All bedroom 
furniture in three bedrooms, except beds, was over- 
turned. Every bottle lid was screwed off or loosened, 
even new bottles. Eighty-five percent of glass and 
pottery broken, including 'Melmac' Moderate-to- 
severe plaster cracks in walls and ceilings of every 
room. Ninety-nine percent of block walls down, in- 
cluding reinforced walls. I have only slight damage 
to my house, but [one-] half block away, every other 
house is condemned; one block away, 90 percent of 
the houses are condemned. All the waterpipes and 
many of the gaspipes had to be replaced in a 36- 
block area of San Fernando where I live." 

1942 Chivers Street (northeast of Glenoaks Boule- 
vard, about 2 miles southeast of Olive View Hospi- 
tal) .• — Fractures were in earth. "According to the 
U.S. Geological Survey, the lot was shortened by 
about 1 foot. Water and gaslines in street broken. 
Most concrete block fences knocked down." 



Felt Area and Intensity of Earthquake 31 



Foothill Boulevard and Vaughn Street (about 
one-half mile east of San Fernando Airport) . — 
"Building about 6 months old. Floor is up and down 
12 inches in a rolling manner. Vaughn Street is 
raised at least 12 inches near rear of the building. 
Side walls torn loose from glued-laminated beams. 
Rear lintel broken. Front wall (SW.) looks good. 
Waterpipe in street (24-in. diameter) broken." 

Northeast of Foothill Boulevard (about one-half 
mile northeast of San Fernando Airport) . — "Build- 
ing (concrete tilt-up) at 12300 Gladstone moved 12 
inches into building at 12314 Gladstone , ground and 
all, at west corner. This was possible because it sat 
back about 12 inches behind adjoining building. 
The 12314 Gladstone building (concrete block) was 
only moved 4 inches off footings at west corner. 
Floor badly distorted. Compression lines in rear yard 
running north-south. Building about 3 years old. 
Street buckled. At 12424 Gladstone (building about 
1 year old) , northeast rear wall failed because nails 
pulled through 1/9-inch plywood roof diaphragm. 
Nails also pulled through plywood on southwest 
wall. Southwest block wall, supported by frame and 
stucco office in front, did not fail, but front block 
corners were completely broken. Building leaning 3 
inches to west. Diagonal east-west cracks in floor 1 
inch wide." 

12401 Filmore (about 1 mile southeast of San 
Fernando Airport, Filmore and Foothill Boulevard, 
northeast of Glenoaks Boulevard) . — Ground was 
cracked, landslides occurred, and water was dis- 
turbed. Chimneys were overturned. Furniture was 
broken. Damage was great. "Mobile home, 60 by 20 
feet, weight 1 1 tons (with wheels off) , moved 4 feet 
and was broken apa*rt. Water and gas pipes in 
ground were twisted and broken. Noise was over- 
whelming. Personal feeling was one of resignation to 
the inevitable — surprised to be alive after shock was 
over. Also complete panic after the shock was over 
due to no communication. Learned later that a fault 
was located about 200 feet from our home." 

Glenoaks Boulevard, southeast of Hubbard Street 
(Brown's contracting yard) . — Heavy lathe moved 9 
feet toward north, leaving straight skid mark. Loco- 
motive (1880 vintage) , standing on rails and ties in 
yard, was overturned (California Institute of Tech- 
nology 1971). 



Sylmar: 

12939 Gladstone Avenue. — Ground was cracked, 
landslides occurred, and water was disturbed. Chim- 
neys and water tanks were cracked, twisted, and over- 
turned. Plaster and windows were cracked. Furniture 
was broken. Damage was moderate to great. "Land- 
slides in the hills." 

13972 Sayre Street (between Borden Avenue and 
Foothill Boulevard, near Phillippi Avenue, south- 
west of Foothill Boulevard) . — Ground was cracked, 
landslides occurred, and water was disturbed. Houses 
were off foundations; cement slabs were cracked in 
half and spread. Damage was moderate to observer's 
home. 

14141 Foothill Boulevard (about three-fourths mile 
southeast of Olive View Hospital) . — Ground was 
cracked, landslides occurred, and water was dis- 
turbed. Pipes were broken. Hot water heater was 
torn from wall. Wall was moved. Plaster was 
cracked, broken, and fallen. Furniture was over- 
turned. Small objects were thrown. "All animals pan- 
icked; horses broke corrals. The earthquake shook, 
rolled, and heaved. Fires broke out everywhere. All 
birds left at dawn before the shock hit." 

13477 Bradley (northwest Sylmar area, between 
Roxford Street and Foothill Boulevard) . — "Limbs 
on my trees were shaken off. My block wall fell. 
Vehicle moved about 2 feet. In the community there 
were many chimneys down and some houses were off 
foundations. Little plaster cracking in my home and 
no windows were cracked. Damage to my home was 
slight." 

1544$ Cobalt (west Sylmar area, near San Fer- 
nando Road, south of Roxford Street) . — Ground 
was cracked and water was disturbed. Chimneys and 
tombstones were overturned. Damage was slight at 
residence (mobile home) . "I was never so frightened 
in all my life. I have never been a nervous person, 
but during these last 2 months I get scared at the 
least little movement." 

13^97 Simshaw Avenue (about six blocks south of 
the southeast boundary of the Veterans Administra- 
tion Hospital grounds) . — (Excerpted from a letter to 
Robert D. Nason, Earthquake Mechanism Labora- 
tory, ERL, NOAA.) "The first shock was sudden; no 
warning rumble. I thought it was an explosion. We 
went up and down, with the noise and jolts acceler- 



32 



San Fernando Earthquake of l'J7l 



ating. I can recall lour very hard up and down mo- 
tions, the last one being the hardest. I he- sound 
seemed earsplitting I thought my eardrums would 

burst. Il was impossible to lieai anyone, so we jusl 

didn't bother. My daughtei said slie was screaming, 
but not one of us heard her. My husband, a large 
strong man, tried to lone himsell up bom the bed 
but was slapped down each time. Five times he tried, 
straining with every muscle, until he was exhausted. 
I bad trouble hanging onto the bed. We could heai 
nothing but the noise ol the eai thquake. I he slapping 
motion of the earth seemed to be in an east west 
direction, with the last slap ending in a hard motion 
to the west, towaid Olive View Hospital. We weie 
shaking between the up-and-down motions. Now we 
started to roll. I was holding onto the bed loi 'dear 
life' to keep from being thrown into the furniture. I 
could see the (lock glide acioss the loom. I looked 
out the window from the bed. The window starts at 
5 feet from the floor and goes to about l i /, leet from 
the ceiling. I could clearly see the outline of the 
trees against the sky (it is a 360-acre area, rather 
open) , the tops of the trees, the sky, the daik area of 
growth, and the very dense area — I expected to see- 
the ground any minute. This was repeated with 
every roll. At one point I thought the house would 
go over with the next roll, as each roll was worse 
than the last. That, 1 believe, was the end of the 
major motion, as my husband and I jumped out of 
bed almost simultaneously. It was when we were in 
the rolls, north-south direction, that I could hear 
everything falling and breaking. The 'slaps' felt as if 
one were being blown around and up in the air, 
then coming down hard, like being in the center of a 
big explosion. The concussion was unbearable. Dur- 
ing the rolls the sound was much more bearable. 
When we got to the bedroom door we found it was 
jammed with furniture, including the dresser, which 
weighs about 250 pounds, and the sewing machine, 
which was upside down. The minute I could get a 
few inches gap in the door, I yelled to my children 
to get outside, and not to wait for us. My husband 
had the door cleared in seconds. My four children 
were huddled in the hall. We were now in the after- 
shocks. The hall was leaning in first one way, then 
another. We pushed the children down the hall. We 
were thrown against each side of the wall all the way 
to the front door. Then came another hard after- 
shock, and my husband could not get the door open. 
As it eased up, he was able to jerk the door open, 



bending ihe middle hinge badly. W< fust 

ones out on OU1 Street. We stood on the lawn and 

watc lied Pacoima Dam light up with a hazy glow and 
then lade. Ihe light cam* from behind tb< front of 

the- dam aiul was a steady light, ne>t a flash , and | 
Were hits ol slides and dust. We could heai lejts (A 

locks Milling down ejff the dam area, and 
thought the- clam was breaking. We left the- children 
in the car, which was bouncing up and down with 
e\ei\ shake-. I»v now. people weie stalling te; cOfDC 
out o\ their houses. I just sat in the middle- <>\ the 
yard, I was so dizzy and dazed. I he- ground was 
bumping up gently, and I noticed that I was sitting 

on one- e,| ihe c lacks in the \aid but I just didn't 

i.ne I saw people whej looked simply frightened enit 
of theii li\es and some who looked absolutely blank. 
We- fell as though we had been through an explo- 
sion. It wasn't until we weie in the aftershocks (in 
the hall) that I suspected it was an earthquake. We 
returned to the house- a minute or two at a time to 
gathei shoes and ie)bcs. It took us 2l/£ hours to find 
my husband's glavses even thejugh fie knew where he 
had left them. At daylight, we were amazed to find 
the house structurally intact, as we had been think- 
ing it would be totally ruined. Inside, however, it 
was a mess, taking over 3 weeks to straighten it up. 
The house has a slab floor and dry walls, and stood 
up well. We had about SlHl in structural glass dam- 
age, even the shower doors were broken. Our neigh- 
bors on both sides of us were not so lucky. In gen- 
eral, things were scattered in a very even pattern 
throughout the house. I took a straight pin, which 
was embedded about half way in, out of my bed- 
room wall. I have written down most of the details 
as I remember them and given a lot of thought to 
them, trying to be as exact as possible, if anyone 
could be exact through it. I a^ed my doctor how Pa- 
coima Memorial Lutheran Hospital was and he said, 
'Bombed!' Somehow that just explains things per- 
fectly." 

13284 Hubbard Street (about 1 mile south of the 
Veterans Administration Hospital) . — "I had just got- 
ten out of bed, and was immediately thrown to the 
floor. Xo warning at all — one minute I was standing 
and the next minute I was on the floor. I couldn't 
have gotten up if I had wanted to. I don't remember 
any ground noises, just the sound of furniture and 
glass breaking. Almost everything of glass in the 
house was broken. Cupboard doors opened and all 
dishes fell out. Our heavy kitchen refrigerator was 



Felt Area and Intensity of Earthquake 



moved nearly 1 1/ 2 feet; television tipped over; heavy 
gun cabinet tipped over. All the furniture was 
moved a foot or more from the walls. Our fish pond, 
7 by 8 feet and 18 inches deep, was almost emptied. 
I don't know what kind of ground we are on, but it 
must be pretty solid because the only damage to our 
house was a few hairline cracks on the outside plaster 
and one very small crack in the kitchen ceiling. We 
didn't even have a broken window. Our big pickup 
truck, with a big camper on it, was moved about 2 
to 3 feet. All the chimneys in the area were shaken 
down and all the block walls were down. Some 
houses just across the street were damaged and de- 
clared unsafe. I would say the ground here is level. 
There was no ground cracking on my property, but 
the street in front has cracks in the asphalt and all 
the street corner curbs seem to be cracked or broken. 
I wouldn't go back in the bedroom for about 2 
weeks because when the shock was going on I felt 
trapped in there. The people in the community are 
still being frightened by the aftershocks." 

About 3 miles northwest of Sylmar (in canyon on 
Highway 14 at the Los Angeles city limits) . — "I was 
reading the morning paper when the shock hit. All 
other earthquakes that I have experienced were of a 
rolling motion, but this one felt as if the bottom fell 
out of everything. I felt a falling sensation, and 
jumped up to try to get out, but I was knocked 
down to my knees. I was sitting at the kitchen table 
when it struck. Everything began to fall; all dishes 
and glassware crashed to the floor; then in about 5 
seconds the light went out, and lor 30 seconds I 
couldn't move. I put my hands over the back of my 
head and stuck it under the table because bottles 
and everything else were falling and hitting me on 
the head. I thought it was the end of the world. My 
wife hadn't gotten out of bed yet, and she began to 
yell that 'the windows are breaking and the house is 
falling down.' I finally got to my feet, after about 30 
seconds, and yelled to my wife to hurry down so we 
could get outside. If we had been sitting on a big vi- 
brator, it couldn't have shaken us any harder. There 
was no rolling or horizontal motion. It was a 
straight-up-and-down motion. A big bookcase and a 
large commode upstairs fell toward the east. We 
have two large china closets in the dining room and 
there was not even a dish or glass broken in them 
during the whole thing. This old house was built in 
1915 and is on pretty solid ground. There was no 
noise as in other earthquakes I have experienced. 



This one hit without warning. My service station 
across the street from me was not damaged either. 
About one-half mile south of me, near that new free- 
way that was being built and where so many bridges 
were lost, there is a mountain that is torn all to 
pieces — looks like it went through a grinder. The 
north side of my place didn't seem to get hit as hard 
as the south side." 

Kagel Canyon Area: 

Los Angeles Fire Station No. 74 (12587 North 
Dexter Park Road, about 3 miles southeast of the 
Veterans Hospital, in sec. 32, T. 14 W., R. 3 N.) .— 
Ground was cracked, landslides occurred, and water 
was disturbed. Chimneys, tombstones, elevated water 
tanks, etc., were cracked, twisted, and overturned. 
Gas mains were broken. Power was turned off. Fur- 
niture was overturned and broken. Violent motion 
occurred in all directions; also strong vertical mo- 
tion. Damage was great. "This building was moved 
off foundation approximately 12 inches and had to 
rise over sill at least 4i/£ inches to settle down with- 
out damage to the shingles." The following is an ex- 
cerpt from page 177 of the paper by Morrill (1971) : 
"Firemen were resting in the wood frame quarters 
building. . . . Mr. J. White, duty fireman, stated that 
he was tossed out of bed onto the floor, and the bed 
landed on top of him. Every object in the building 
was upset. Even the handset of a standard wall 
phone came off its hook. Loud cracking and thun- 
derlike noises added to the general confusion. The 
building was shifted off its foundation. Outside, 
rocks were thrown off the ground, and large cracks 
appeared in both soil and rock . . . many ground 
cracks appeared throughout the area. The surface of 
a hill adjacent to the building exhibited the 'shat- 
tered earth' effect ... a few miles to the west. A 
nearby rock roadcut appeared to have exploded, and 
the adjacent road was offset in many places. A 20-ton 
fire truck enclosed in the garage moved 6 to 8 feet 
fore and aft, 2 to 3 feet sideways without leaving vis- 
ible skid marks on the garage floor. The truck was in 
gear, and the brakes were set. Damage to the truck 
was a bent rear step, broken windshield, shattered 
red light, and siren broken off. Also, a ladder and a 
hook were broken. Marks which appear to have been 
made by the right rear tire were found on the door 
frame 3 feet above the floor, while the metal fender 
was not damaged. The fender extends several inches 
out beyond the upper portion of the tire. Four feet 



:;i 



.SV(// Fernando Earthquake o\ 1971 



above the flooi the 1 1 < >s<- rack was broken by 1 1 • * - real 

step ol the 1 1 in k . The step was beni up, while 1 1 k- 
hose rack was broken downward. The real oi the ga- 
rage was pushed outward 6 to N iii( lies, and the final 
position ol the truck was aboul 1 feel oui the- from 
of the garage, with the garage dooi resting on the 
cab." Morrill (1971) also suggests that the building 
accelerated upward, with respeci to the ground, at a 
rate of at leasi Ig foi about 0.1 sr< ond. 

Kagel Canyon (from a lettei by Doreen Russell, 
Secretary, Kagel Canyon Civu Association). — ". . . 
many ol our homes have been totally destroyed, 
while others just next dooi had no real structural 
damage. For example, oui home had very slight dam- 
age, but two of our immediate neighbors, one [who 
owns] a very new house and the other a mm h oldei 
structure, lost their homes. Severe ground scarp at 
(den I faven Cemetery." 

Kagel Canyon (IIS2 Z > West Trail, southern K 

Canyon). — "We were too busy to he scaled, until 
later. We were already up. Husband heard the shock 
coming- and thought it was a low -living jet. Hard rat- 
tle first, then in 1 to - seconds I was thrown from 
chair and my husband was dumped into the tub; 
then bac k-and-lorth motion. I was able to reach the 
hall and get the children into a doorway until things 
slowed down, then we went outside. Lights went out 
in the first movement. Water out but gas and tele- 
phone were OK. Ground seemed to keep moving. 
We have three acres (San Gabriel Range, Inst moun- 
tain by valley) , with three houses. Lower house had 
little damage; no landslides or broken pipes. The 
second house, about 125 leet or so higher, had a 
cracked foundation; 1-foot-thick walls cracked 1 to 4 
inches; four deep ground cracks, two under the 
house. Third house, about another 100 feet higher 
up than the second house, had cement floors buckled 
and cracked; deep ground cracks; pipes separated; 
new garage (side room) separated from house and 
slightly askew; %-inch floor crack in cement; door 
wedged closed; everything dumped from cabinets, 
and lots of stored glass windows broken. Garage was 
a mess. Water main in front of this third house was 
broken, separated inches in five places, as it curves 
around the corner." 

Kagel Canyon (13706 North Kagel Canyon 
Road) . — "Water tank off foundation. Natural stone 
wall (no mortar) fell. Ground cracked. My husband 
was awake and was thrown from north to south. Fur- 



niture was overturned from north to loutl 

t. Refrigeratoi was out of j>om- 
tion from south to north about \h inches, kitchen 

cabinets, from both north and south she. <■ al- 

most emptied. In living room, articles on north 
ol room slid off tables toward north, and on south 
end ol room all books were dumped onto the floor 
from west to cast. Most violent action seemed to be 
from east to west, lioin final position of luiniture." 

Karl Holton Boys Camp Cm Mini Canyon about 

3l/£ miles southeast ol the Yeteiaus Hospit ■ ■■ 

tensive- damage occurred to buildings. One hundred 
and fifty feet o| 1 1 foot-high concrete bloc k wall col- 
lapsed. Extensive lands! iding and fracturing resulted. 
Severe structural damage occurred where ground 
ciacks passed through or were adjacent to the build- 
ings. 'I he c amp was e\ac uateel. 

Little Tujunga Rangei Station (1237] North Lit- 
tle Tujunga Canyon Road, about \ 2 mile south of 
Kail Holton Boys (amp: report Ircjin Hugh E. 
\lasteison. Distiiet Fiic- Control Officer). — "Ground 
heavily fractured. Water tank twisted. Concrete less- 
pool, waterlines. and pavement damaged. Everything 
upside down. Vei\ heavy damage to all the buildings 
at the station. Main inspectors have been at the sta- 
tion but no final estimate made of the damage; how- 
ever, it will probably exceed SI million. All crockery 
and china broken." 

Little Tujunga Canyon Road-Bear Canyon Area 
(Bear Divide Ranger Station. N\V i ,. sec. 7. T. V 
R. 1 I \V.. about 1 i , miles north-northeast of Pacoima 
Dam). — "Rockslides cm road up to 500,000 cubic 
yards. Main ground cracks. Block wall broken. Mo- 
bile home dead-manned from concrete to l 2 -inch 
cable to %-inch eyebolts — eyebolts straightened out. 
Water sloshed out ol toilet bowls. Many cracks in fill 
ground and solid ground. A giant up-and-down mo- 
tion, changing to a north-south side motion." 



INTENSITY VIII 

Granada Hills 

Van Gogh Street Elementary School in the upper 
Granada Hills area sustained structural damage 
caused by ground surface movement. Patrick Henry 
Junior High School in the lower Granada Hills area 
sustained structural damage caused by vibrational 
movement. 



Felt Area and Intensity of Earthquake 



35 



17201 Courbet Street (about three-quarters mile 
west of Upper Van Norman Reservoir) . — Twisting 
and fall of chimneys, columns, and monuments oc- 
curred. Damage was great to masonry and concrete. 
Dishes, windows, and furniture were broken. Cracks 
were found in plaster, windows, walls, chimneys, and 
ground. 

16834 Bircher Street (southwest of Lower Van 
Norman Reservoir) . — "Our tract (wood floors, lath, 
plaster, and stucco; one- and two-story homes) suf- 
fered minimal damage. However, newer dwellings to 
north and northwest (slab, wallboard construction) 
sustained major damage; many condemned. Holy 
Cross Hospital is about 2 \/ 2 miles east and the Van 
Gogh School is about 1 \/ 2 miles north of our home. 
Many commercial markets had major-to-minor dam- 
age; many business buildings marked 'unsafe.' Minor 
ground cracks north of our tract. Block fences fell. 
China cabinet overturned. Damage slight at my 
home." 

10518 Encino Avenue. — Ground was cracked, 
landslides occurred, and water was disturbed. Chim- 
neys, tombstones, elevated water tanks, etc., were 
cracked, twisted, and overturned. (This observer also 
reports only slight damage.) 

17608 Blackhawk Street. — "No observed fissures, 
faults, or landslides. Most 4-inch-thick concrete block 
walls in neighborhood (running north-south) are 
down. East-west walls seem pretty good. All cup- 
boards on east-west walls emptied. Thirty-gallon 
water tank shifted 3 inches S.70°W. Several i/^-inch- 
thick cracks at attachment of garage to house and 
around bottom plate. Damage moderate." 

12038 Bambi Place. — Ground was cracked. Chim- 
neys were damaged in neighborhood. Bookcases were 
moved 6 to 8 inches. 

12817 Neon Way. — Ground was cracked. Cement 
and plaster were cracked. Furniture was broken. 
"Everything affected." Damage was slight to moder- 
ate. 

16939 Cohen Road. — Block walls were cracked 
and broken. Plaster was cracked and broken. Chim- 
ney and concrete block wall were cracked and 
knocked over. Toilet bowl was broken. Furniture 
was overturned. "Damage slight." 

16329 San Jose. — Chimneys were overturned. Two 
feet of water slopped from swimming pool. Plaster 
was cracked. "There was quite a lot of vertical move- 



ment during the first part of the shock. It was almost 
impossible to walk for the first few seconds. I tried 
to walk and felt as if I were walking uphill." Dam- 
age was slight. 

15832 Chatsworth Street. — Foundation, driveway, 
and water pipes were cracked. Chimney broke at 
roofline. Two ceilings of tile fell. One light fixture 
and all pictures and mirrors were down; shelves and 
cupboards were emptied. "Outside damage limited 
to west side. Our biggest bother was sorting and re- 
turning several thousand books to shelves. The 
shelves (fastened to the walls) were not damaged, 
just emptied. The later additions to the house were 
finished with wallboard — all seams cracked and must 
be redone. All the plumbing in one bathroom 
broke." 

10342 Odessa Avenue. — Block wall was collapsed. 
Driveway was cracked. Rock facing in decorative chim- 
ney was cracked. "Our home and community is lo- 
cated about 3 to 5 miles from the hardest hit areas of 
Sylmar and San Fernando. The house faces in a 
northwesterly direction, and during the shock it 
seemed to move north-south. Our driveway break 
(minor) is also from north to south. The block wall 
which collapsed in yard runs east-west. Our neighbor 
also commented about the north-south movement, al- 
though their home faces south and runs east-west. 
Based upon the condition of the interior of house 
(fallen lamps, books, and dishes, etc.) , it seemed 
that the front side (west) of house moved more than 
the back side. There was little displacement of ob- 
jects on eastern side, but much on western side. Af- 
tershocks have also seemed to move the house north- 
south, with only occasional east-west shocks. 
Although the aftershocks have decreased considera- 
bly in the 3 weeks since the main shock, I find the 
most disconcerting problem now is the continual 
popping sounds in walls and cabinets, sometimes very 
loud, and the creaking and springy feeling of the 
floors. I do believe so many homes in our area came 
through the earthquake so well because of our wall- 
board interior walls. Many of our friends who have 
lath and plaster did not come through the shock 
nearly so well." (There were also six reports of in- 
tensity VI from Granada Hills.) 

Mission Hills 

No address given. — Ground was cracked, land- 
slides occurred, and water was disturbed. Chimneys, 



36 



San Fernando Earthquake <>\ l'J7l 



tombstones, and elevated watei tanks were cracked 
and overturned. Plastei cracked, broke, and fell. 
Windows were cracked. Furniture was broken. Dam- 
age was great. 

Mission San Fernando Key (about one-hall mile 
south of the Holy Cross Hospital). — Adobe walls 
were severely cracked. 

10222 Norwich Avenue. — Heavy objects (30-lb 
tape recorder and large outside plarrter) were 
thrown 3 to 4 feet and overturned. Six-year-old boy 
was thrown out of bed. light objects were rrot 
rrtoved. "Noticed high-frequency, low-amplitude verti- 
cal motion at beginning of shock; low-frequent y, 
high-amplitude lateral motion at end." 

Newhall— Valencia Area 

Newhall 

Four old buildings in downtown Newhall were 
condemned by the city engineer who estimated that 
90 percent of the fireplaces and chimneys on two- 
story houses were damaged in the area. One concrete 
wall was knocked clown; most homes sustained only 
superficial damage (National Earthquake Informa- 
tion Center 1971) . Gasline broke on Lyons Avenue. 
An observer at Honby reported the Newhall tele- 
phone plant was flooded, the result of a broken 
water main. A glass manufacturing company (be- 
tween Newhall and Saugus) sustained $10 million 
damage to buildings, storage bins, and furnaces (Cal- 
ifornia Institute of Technology 1971) . There was 
also damage to oil refinery storage tanks and pipe- 
lines at the Newhall refinery located about 2 miles 
southeast of Newhall. The bottom of one jet-fuel 
storage tank buckled, and there were scattered leaks 
elsewhere in the refinery. The chief problem for the 
refinery was lack of water. Both sides of a booster 
pump on the waterline leading to the refinery were 
ruptured. Minor damage was done to testing equip- 
ment in the laboratory (Anonymous 1971) . 

18909 Sierra Estates Drive (about 5 miles north- 
east of Newhall Post Office, south of California 
Highway 14) . — Water supply was cut off. Some 
chimneys were loosened from homes; cracks occurred 
in walls, concrete slabs, etc. China closet was over- 
turned. Many windows were broken in stores. Dam- 
age was great. This observer gives "place" as New- 
hall, Soledad, and entire area. 



26961 li Avenue of the ()ak\ <nor tlieast Newhall 
area, aboul '> miles northeast o! Newhall 
Office;, (.round was cracked and water was dis- 
turbed. Side walls were lifted and shifted, retaining 
walls were- tilted. Dry walls had few crack*. Furniture 
was shifted and overturned. Shock was like a drop- 
ping motion, then a shift from northeast-yjutl. 
Large (19-in.) television thrown off Mbot-high 

stand. Bookshelves and books on floor ; lamps thrown 

to floor; kitchen cupboards emptied of all contents, 
canned goods, dishes, etc. Kelngeraioj doors thrown 
open and contents slid out cm floor. Large ci. 
(on short legs), full of material, shifted about 9 
inches on carpeted floor. Had to leave premises due 
to my wife being disturbed." 

21 ^22 Walnut. — (.round was cracked, landslides 
occurred, and water was disturbed nearby. Chim- 
neys, tombstones, and elevated water tanks were 
cracked, twisted, and overturned. Plaster was 
cracked. Furniture was broken. Moderate damage oc- 
curred to house. 

2(7 36 Walnut. — "We were not at home during the 
earthquake, but when we returned home we found 
beds, heavy bookcases, the stove, dressers, etc., had 
all shifted; one bookcase was overturned. Top of 
chimney, to about 4 feet below the roofline, broke 
off and fell, and made a dent in the lawn about a 
foot deep. All rooms except the kitchen have cracks 
in walls. Outside concrete slab is cracked. No broken 
windows." 

Newhall Ranger Station (about 1 mile south of 
Newhall) . — Ground was cracked; pipelines were bro- 
ken. Chimneys were cracked and bricks "rear- 
ranged." Plaster was cracked. "Cracks in plaster and 
paneling of not much significance. Damage slight. 
This site is a 1-acre area housing compound of the 
U.S. Forest Service administrative buildings. The 
structures, two offices, one 6-bay garage, one bar- 
racks, several small outbuildings, and one residence, 
were constructed in 1934 and are of wood; very well 
built. All doors and cabinets in the residence and 
offices were thrown open and contents spilled to the 
floor. Direction of thrust appeared to be to the 
south. No furniture of any appreciable size was 
knocked over, but very heavy pieces were shifted sev- 
eral inches. Electricity, phone, and water services 
were knocked out at impact. Hairline cracks are ap- 
parent in and on all of the buildings, but appear to 
be the result of aftershocks." 



Felt Area and Intensity of Earthquake 37 



23405 La Glorila Circle. — Patio block walls were 
loosened. Piano and refrigerator were moved. Plaster 
was cracked over windows and doors, but not very 
extensive. Market, two blocks away, lost its windows. 
Damage was slight. 

Valencia 

24200 Lyons Avenue (shopping center, east of 
Golden State Freeway) . — Suspended ceiling col- 
lapsed. Nearly all glass in wall was broken (U.S. 
Geological Survey and the National Oceanic and 
Atmospheric Administration 1971). 

25310 Via Calinda. — Chimneys were cracked, 
twisted, and overturned. Water was disturbed. Chan- 
delier fell. Television was overturned. Small amount 
of plaster was cracked. Windows were cracked in 
nearby houses. "In the city of Newhall block walls 
were knocked over." Damage was moderate. 

25349 North Avenida Ronanda. — Chimneys were 
cracked, twisted, and overturned. Garden walls were 
down. Furniture was shifted and overturned. "Sensa- 
tion of violent rotary motion." 

25657 Avenida Jolita. — Chimney was separated 
from house. Some plaster was cracked. Furniture was 
shifted, overturned, and broken. Damage was slight. 

Saugus and Soledad Canyon Areas 

Saugus. — Ground was cracked. Trailer foundations 
were cracked. Most light fixtures fell. Furniture was 
shifted, overturned, and broken. Plaster cracked, 
broke, and fell. Windows were broken. "There were 
eight people working in the post office at the time. 
Everyone got out just in time to avoid falling light 
fixtures. Equipment was tossed around more in our 
trailer complex (seven trailers placed together) than 
it was in our main office (brick building) . The crew 
maintained their composure, as far as I could see, 
but it was the general consensus that if the shock 
had lasted much longer, panic would have resulted." 

Soledad Canyon Road Areas — Honby Area (about 
l\i/ 2 miles east by north of Saugus) : 

19419 and 19407 Soledad Canyon Road (North 
Oaks and shopping center) . — Roofs were collapsed. 
Cracks were found in nearby parking lot (U.S. Geo- 
logical Survey and the National Oceanic and Atmos- 
pheric Administration 1971). 

27327 Camp Plenty Road (just north of Soledad 
Canyon Road) . — Six-hundred-pound transmitter was 



overturned to south. Bookcase was overturned and 
others moved. Plaster was cracked. "All plasterboard 
joints show cracks. Some vertical cracks in founda- 
tion. No ground cracks here, but shopping centers 
close by (.'500 yd) have cracks in blacktop parking 
lots. Roof collapsed on north side of W. T. Grant 
Building. Fifty to 70 percent of store windows 
broke. Highway bridges need repairs to approaches. 
Electricity off instantly, but it came back on again in 
about 20 minutes." 

Honby School. — Ground surface cracking was evi- 
dent throughout the site. One crack passed through 
one of the school buildings (U.S. Geological Survey 
and the National Oceanic and Atmospheric Adminis- 
tration 1971) . 

27430 Fairport Avenue. — "All I have spoken with 
said it felt as if their building would topple. We 
have a 1 6-foot trailer parked in driveway and it 
twisted or jumped over a foot around. Block walls 
fell. In the community, streets cracked, curbs broke, 
and many buildings were condemned. I teach at the 
Honby School (one-story building; six classrooms) 
— over I -inch-wide floor crack across center of slab; 
section dropped about \\/ z inches; some doors will 
not open and some will not close; new blacktop bro- 
ken and cracked. At my home (front faces west) , a 
front door latch (locked) broke off. The door was 
opened but held by safety catch. Many people have 
asked for transfers for their children and are leaving 
the community." 

27416 Dewdrop. — Ground was cracked. Chimneys, 
tombstones, elevated water tanks, etc., were cracked, 
twisted, and overturned. Many cracks were found in 
swimming pool. Plaster was cracked. Furniture was 
broken. Damage was moderate. 

2S1S9 Hot Springs Avenue (north Honby area) . 
— Block walls were flattened. Chimneys were cracked 
and twisted. Stucco was cracked. Small (14-in.) 
ground cracks were evident. Building was bounced 
in all directions. Locked doors swung open and 
closed. Damage was slight to building. 

Near Soledad (10 5 11 Soledad Canyon Road, about 
7 miles east by north of Honby) . — Ground was 
cracked, landslides occurred, and water was dis- 
turbed. Chimneys were cracked, twisted, and over- 
turned. Roof was split (wooden building) . Furni- 
ture was shifted, overturned, and broken. Water 
heater was torn loose. Damage was slight to house. 









S ('mint iO.iNt ot Honb) S :\.-n 

School vi.i> damaged by ground surface movement 

g Ik tut 
the school i UJS S I the Na 

tional O i.inu and Attn- i \ . 

. 

in Ii«>n I 
— The press reported that house and land "slipped" 
more than SO feet and that Head Road in I 
yon dropped 15 feet. 

intensity \ ii 

turned. "F.arth- 

te appeared to have long dura: lit 10 to 

15 minutes, due to afti Noticea 

down motion P. . d build- 

in busu rid where some plate 

ere broken: ow building 

tpet walls and front. M Dan.. \ ght in 

the Alhambi d frame buildings 

age was limited : od windows, and 

ken dishes and knukktu ^ re buil 
suffered broken plate g B windows Chimneys 
pullc m some bu gs v?\eral unrein- 

parapets fell." The press :ted that 

pouerlines were The 

publich 
owned stnu : 

buildings demolished or to 
bede sdamajj ind estimated 

|S million cxg 

intensity VI a uty 

i 

:denm. — Chimnevs fell. "Aim a 
shocks jtinguis 

gen ^crashing 

lilure in after- 

• '.-"•• erv thing tall fell, lamps 

\ ... 

on Lake Avenue. H 

builo , Pasadena . I: had fallen 

ks from she 
rigs in cupboar 
hall fell . problem. E 

Pasadena n the phone : 

€ schx> - alls cat: eneral alarm 

reflected in phone calls but no panic of a 

g d teetered and crashed if i 
Some people 



>ere 



ime uii 

in Altai : nd 20 

a queasy 

e mitia 

ips.' cr in p»ol splashed 

t ; ; 1 i rat Led The pre 

ed that poweiiinej were d< 

VI and six re;- were 

reveued from the ar 

Beverly HUL — The 

- et al. I 3 t lude publicly ov 

Ntitu tun 

buildings d< r to be demolished: 1.000 

uatcd total dollar loss at 
100 rhert were : ur reports of intensr 
and four rep«rts of intensit\ V from the Beverly 
HiUs 

bank. — Chimm ed. and 

overturned. .inreinforced b: 

Flev id phoi I and 

fell. Wis >ere broken. Heaw furniture was 

ed. 'I ha\e checked approximate'^ 12 bom 

.d found no 
:ural d.v g i>nlv items of interest were the 
I furniture, items falling out of cat 

nd broken windows. Damage 

tnce it r didn't seem 

so bad. We were alive and had suffered verv little 

. in com: i others. The most frighten- 

tftershocks — not knowi: _ 

ins thev would be We 
lived in continual f. .: few da%> Ob- 

reporte 
2 -.borhood is located in southwestern Burbank. 
>n in t - an incr rapid, com- 

-rconds. after 
beir.; tied, A e motion had reac'r 

decrease in intensiry: how- 
, .ind motion did not seem to stop comp' 
until after a co: ..h of time. Brilliant, 

seen in various directions 
( apparer rrrect on powerlines or trans- 

rv prominendy heard in this 
. borhoc. emitted from a powerplar: 

:n here as the quak .lose 

ram shot out. Power was knocked out in this 

. borhood and remained out for slightly more 



Fell Area and Intensity of Earthquake 39 



than 2 hours. In this house a number of things fell 
from shelves or tables, or were tipped over, or 
changed positions (as happened, undoubtedly, at all 
houses near here). A few knickknacks in precarious 
positions seemed surprisingly virtually unaffected: 
however, a water softener tank, just outside the 
house, jiggled off one of its three supports and tilted. 
The tank is too heavy for one person to move with- 
out great difficulty. Nothing in this house was bro- 
ken. Glassware broke at next-door neighbor's house. 
Probablv some things were broken at nearly everv 
house around here, (Incidentally, relatives living in 
ern foothills of Burbank reported figurines in 
glass dome were turned around even though dome 
itself was unaffected.) No windows were damaged at 
our house and none were damaged at most of the 
neighbors' houses. Many ^although not most) plate 
glass windows at nearby business establishments were 
broken. A substantial number (about 10 percent) of 
chimnevs in this neighborhood were cracked, several 
so severely that their upper portions had to be re- 
moved. A few chimnevs were slightly separated from 
houses, and the upper portions of a few were very 
slightlv twisted. Our house had no obvious damage. 
The walls of our next-door neighbor's house devel- 
oped some narrow cracks in various places. Narrow 
cracks developed in walls, especially at corners of 
windows and doors, in many buildings in this neigh- 
borhood. One straight crack, clearlv visible from the 
street, extended from the base to the roof of a sin- 
gle-storv library one-quarter mile to north, and sev- 
eral long, conspicuous cracks formed in plaster inte- 
rior walls of a church one-half mile to north of here. 
Small chips of plaster fell in several buildings. Some 
garden walls were cracked, several were significantly 
weakened. Damage in other parts of Burbank: In- 
stances of cracked walls, badly cracked chimne\s. 
shattered windows, and other damage were common 
in much of Burbank. Some old buildings had exten- 
sively damaged walls and ceilings and were consid- 
ered unsafe. Some of the severe damage included the 
fall of portions of the exterior walls just below the 
roofs of a church and a rest home, both relatively 
old buildings near downtown Burbank. The walls of 
both buildings were predominantly of brick. Al- 
though the worst damage was typically to older 
buildings, minor damage was common in newer 
ones. In spite of much costly damage in places, at 
many other places in town, damage was virtually 
nil.' - This observer reported that more than 120 af- 



tershocks had been felt up to June 21. The following 
statistics (Steinbrugge et al. 1971) do not include 
publicly owned structures: 445 buildings damaged; 
2"> posted unsafe: buildings demolished or to be de- 
molished include three residential, three commercial, 
one church, and one school: 500 chimnevs damaged: 
and estimated total dollar loss at S4 million. (Eight 
intensity VI and three intensity V reports were re- 
ceived from the area.) 

Canoga Park. — Exterior building walls were 
cracked. Windows were broken. Plaster was cracked. 
One observer stated: "The building is a small shop- 
ping complex. One of the stores sells liquor and gro- 
ceries. Damage to the bottles was extensive — 40 per- 
cent of the stock fell off the shelves, even though 
there were wires to prevent this. The outside walls 
of the building cracked and separated about three- 
quarters inch at some places." The following is an 
excerpt from Headlines (1971). a May Company 
publication, reporting on damage at the May Com- 
pany Store in Topanga Plaza: "Twentv-five plate 
glass windows in the escalator well shattered. Ap- 
proximately 50 percent of merchandise and display 
fixtures damaged or destroyed in china department. 
The bedding and linen stockrooms were a tangle of 
toppled shelving and merchandise. Ceiling tiles and 
complete light casings fell. On the roof, four 4-ton 
tans were sheared from their bolts, and the fans 
moved 2 to 9 inches out of position. The lamp. 
mirror, picture, and television departments also re- 
ceived extensive damage to merchandise. The lower 
level and middle level also received damage. The 
major problem was water. Three inches of water had 
seeped into these levels by midmorning as the result 
of damaged water pipes in an adjacent department 
store in the shopping mall. The building was care- 
fully inspected bv engineers and building inspectors 
before store members were permitted to enter. Dam- 
aare to the structure was only surface damage, and 
the building was found to be in good condition." 
"Movement seemed to be north-south and west-east." 
"Our home was shifting so violently that it was diffi- 
cult to walk." Another observer reported: "Water 
escaped from street hydrants. Electricity off 1 hour. 
Awakened by mild rolling shock of several seconds' 
duration, pause of a few seconds, then a sharp jolt 
followed by violent shaking in all directions, both 
lateral and vertical. The intensity appeared to in- 
crease in a continuous manner, with a continuous 



•10 



San Fernando Earthquake <>j l'J7l 



increase In 'thumping-type' noise, and was followed 
by the steadily increasing noise from tailing books, 
then loudei crashing noise o| objects Falling. The 
intensity built up during a period ol SO to 00 see onds, 
then abruptly stopped; then altei a short pause was 
followed by more milder, rolling shocks. Electric 
power went out at the end ol the violent slio< k 
period. Flashes ol light observed during shocks. I 
lost all sense of direction during violent shaking. It 
was difficult to locate exit door in dark bedroom. 
Immediately aftei the shock a check was made foi 
gas leaks, water leaks, broken electric cords 01 wins 
both inside and outside none were found. No neigh- 
bors observed outside. 1'owei failure apparently gen 
eral in the neighborhood. No structural damage 
noted. Many books fell from tops of bookcases and 
from a shell in one closet. Bookcases did not over- 
turn. One table lamp, \\ Feel tall, in cornet ol living 
room, was found in middle of room about 10 leet 
from its original position. Other table lamp simply 
toppled over. All fallen objects were from locations 
on inside walls. Nothing along outside walls ol house 
fell or moved. Water from aquarium spilled out and 
water from neighbor's swimming pool sloshed out." 
"Ilrick wall fell on neighbor's car. Store windows 
broken. Lost 2l/£ feet of pool water.'' Another ob- 
server gave this account: "I heard a rumbling noise 
just prior to reeling the shock; then it hit. Pre- 
dominantly east-west vibration with some north-south 
motion. Felt more like several quick vibrations, then 
a little slower, then several quick motions, with a 
total response effort similar to a boat action in 
water." Still another observer told this story: "No 
dishes, glasses in cupboards broken or noticeably 
moved. No books from bookcase fell. Lost about 1 j/, 
inches of water from 7-gallon fish tank; light hood 
on fish tank bounced out of place but did not fall off. 
Many pictures otr walls did not move or shift. The 
large, heavy, hanging lamp over dining table swung 
more than moderately but not violently in an east- 
west direction. During the first aftershock, a half hour 
or so later, the lamp swung in a north-south direction 
but not as hard this time." "Shock was felt for a 
considerable length of time. Noises of rattling, creak- 
ing, etc., were continuous. Telephone and power 
were out. Water was running, but during the day it 
became contaminated and remained so for about 1 
day." (There were nine reports of intensity VI and 
live reports of intensity V from the Ganoga Park 
area.) 



Encino \n oljservei reported: "Two palm i 
knocked over. Flagstone and concrete driv< 
cracked; concrete and flagstone pool deck raise*; 

hall inch above pool tile; steel support column ol 

porch roof shifted I '/■< inches out of concrete ha 

by 12- by 20-[inch] garage-roof-support timbei shifted 

about I inch on north end. Damage about $4,000." 

Water lines were broken. Plaster was cracked. Block 
garden walls were broken. Vard was swamped with 
water from pool. Electricity was out. (Three inten- 
sity VI reports were received front the an 

Fillmore. Chimneys and plaster were cracked; 

windows were cracked One observer commented: 
"We lost one building in town, a dress shop, when 
the roof caved in. I wo other business buildings were 
damaged: One furniture store lost part of the roof in 
the rear of the building and a hardware store lost 
part of the- brick firewall on the north side of the 
building. All of the grocery and liquor stores in 
towrr suffered losses when canned and bottled goods 
fell off the shelves and display counters. Electrical 
service was out in the surrounding rural areas for a 
short time, about 5 to 15 minutes." Another observer 
stated: "I was awakened by a terrific shaking of the 
bed and a terrible noise. Seemed as if the house 
would fall to pieces, but the only damage to the 
structure was to an outside brick chimney which was 
separated from the house by about three-quarters 
inch. About 2i/ 2 city blocks away, the side of a two- 
story brick building fell on a one-story frame roof 
and demolished the smaller building. There was 
some damage to an orange packinghouse. The lights 
were out for a few minutes." 

Flintridge (southwest of La Canada; 34°11' X., 
1 1S° 10' W .). — Heavy chimney sheared off at roofline. 
Plaster cracked throughout interior. Minimum crack- 
ing of exterior stucco. Roof tiles shifted and broke. 
Torsion of building visually observed. Interior wood 
and lath and plaster failed (both horizontally and 
diagonally) in shear and (vertically) in tension. Also 
some compression parallel to wave travel. Wall dam- 
age was extensive; ceiling damage was moderate. 
Water sloshed from swimming pool. Small objects 
and books fell. 

Glendale. — Ground was cracked. Chimneys were 
overturned. Plaster and windows were cracked. Fur- 
niture was broken. Electricity was out; street lights 
were flashing. The press reported that the Glendale 
Presbyterian Church, built in 1923, was severely dam- 



Felt Area and Intensity of Earthquake 41 



aged. The First Methodist Church was not damaged, 
but in the 54-year-old former sanctuary behind it, 
towers fell through the roof. "There was a complete 
mess inside the apartment. Bookcases fell. Refrigera- 
tor moved about 3 inches from wall. Bookcase on 
west wall; refrigerator on south wall. One brick from 
the brick bookcase, quite heavy, was thrown about 7 
feet." The following statistics (Steinbrugge et al. 
1971) do not include publicly owned structures: 31 
buildings posted unsafe; buildings demolished or to 
be demolished include 13 residential, 23 commercial, 
and five churches and schools; 3,250 chimneys dam- 
aged; and estimated total dollar loss at $2 million. 
(Additional reports of eight intensity VI's and of 11 
intensity V's were received from the area.) 

La Canada. — Chimneys were overturned. Low 
false ceiling bent and fell. Plaster, windows, and 
walls were cracked; plaster fell. Slab in patio was 
raised and cracked. Heavy objects were moved. Pool 
water was sloshed violently. The press reported that 
powerlines were down. "There was a distinct feeling 
of significant vertical acceleration during the early 
moments of the shock." (Nine reports of intensity 
VI and seven reports of intensity V were received 
from the area.) 

La Crescenta. — Many false fronts of buildings 
were badly damaged. Unreinforced parapet failures 
occurred. Some old stone walls were cracked. Chim- 
neys were overturned. Water and furnace pipes were 
broken. Many windows were cracked in old and new 
buildings. "Cracked concrete pool deck and dislo- 
cated concrete and stone supporting wall." One ob- 
server estimated damage to his house and contents at 
$3,000. "We had very little breakage from dishes and 
knickknacks (5542 Pine Glen Road), probably due 
to the bedrock foundation. Other friends living out 
in the center of the canyon or on deeper alluvial 
deposits had considerable glass and dish breakage. 
One friend on third floor of wood frame apartment 
building had a wall-mounted air-conditioning unit fly 
halfway across the room to the east. I tried to analyze 
direction of motion at my house from swinging of 
lamps and displacement of objects and finally de- 
cided it had to be east-west, even though swag lights 
in bedroom were swinging north-south." (One in- 
tensity VI report and three intensity V reports were 
also received from the area.) 

Los Angeles. — Moderate damage occurred in 
downtown Los Angeles, especially to older type 



buildings with brick and masonry facings. Portions 
of an old building, the Mission Inn, collapsed, kill- 
ing one person. Extensive damage occurred to some 
of the old historic buildings on Olvera Street. The 
press reported "unsafe" and "potentially unsafe" 
signs were posted at some buildings in "Little 
Tokyo" and along Main and Los Angeles Streets. 
Considerable nonstructural damage occurred to some 
of the larger buildings and to some high-rise build- 
ings — plaster partitions were cracked; fall of plaster 
and tile occurred; broken windows were numerous; 
and elevators were knocked out of service. It was re- 
ported that the old Los Angeles High School would 
be demolished due to damage. There were reports of 
ruptured gaslines in Highland Park; and in Eagle 
Rock, it was reported a ruptured gasline blew a cra- 
ter in a freeway overpass bridge (California Institute 
of Technology 1971) . 

Abbey Hotel (82^ West Eighth Street).— "Old, 
poorly built, four-story building. Section about 5 by 
8 feet fell away from lobby wall; waterpipe damage 
at this break. Primary shock was moderate shaking 
for first 5 to 10 seconds, then grew rapidly in inten- 
sity. Stayed at maximum about 40 seconds, with im- 
mediate aftershocks of strong rolling motion, floating 
feeling, and building noise almost ceased during this 
period, only slight creaking noises. It seemed that 
during these aftershocks ground noises could be 
heard, resembling large masses of rock, at great 
depth, being shifted against one another. Some dam- 
age: Cracks, one-quarter to three-eighths inch in 
width, opening on wall corners adjacent to stairway 
entrances on each floor; on ground floor (lobby) , 
plaster fell from ceiling above last flight of stairs and 
adjacent ceiling of area where wall fill and plaster 
fell out. Lights in room flickered on and off during 
the main shake, with floor lamp in great agitation. 
Damage slight to building. Much masonry facing 
damage one block away; much window breakage and 
masonry lacing damage on taller buildings." 

May Company Store (from Headlines (1971), a 
May Company publication, Los Angeles, Calif.) . — 
"The downtown store was closed to store members 
early Tuesday morning while building inspectors, 
store security, and engineers checked every area of 
the store. The building was considered structurally 
sound and safe for entry; but because of the damages 
to the interior, the store remained closed to custom- 
ers. The 'back' stairwell, escalators, and elevator 



VI San Fernando Earthquake of 1971 



wells seemed to have suffered the most dat 

V V alls surrounding the l>;i<k stairs and the walls in 

the adjacent halls sustained much surface damage in 

cracked and fallen plaster, and, in some cases, holes 

in walls and at corners were visible. Main wall sup- 
ports were in good condition and wete not damaged. 
The escalators were extensively damaged. Exterioi 
damage to the store was confined to display windows 
and decorative treatment on the building. Well over 
60 perceni of the plate glass windows were shattered. 
Some slight damage was noticeable on cornices and 
ornamental trim." 

Olympic and Alameda (about 2 miles south by 
east of Civic Center) . — One observer reported: "The 
building in which I work (Olympic and Alameda) 
sustained approximately 400 broken windowpanes, 
14 by 20 inch, all steel sash. Almost 100 percent of 
these were on the north and south sides ol the build- 
ing. One or two freight-type elevators were inopera- 
tive due to guide tracks warping and permitting 
counterbalance weights to swing free." 

127 South Serrano Avenue (in area about 1 y 4 
miles southwest of Los Angeles City College). — Al- 
most all nearby chimneys were badly fractured. 
Many new plaster cracks were found in all eight 
rooms of the house, bookcase fell; dresser was 
moved. Pool water was splashed 20 feet horizontally. 

3812 Terry Street (in area about three-quarters 
mile northwest of Silver Lake) . — Small objects flew 
through the air. Vehicles were rocked (cracked water 
hose to radiator). Plaster cracked and fell; ceramic 
tile was cracked. "Everything in front apartment that 
was movable shifted. Heavy chest of drawers moved 
12 to 15 inches away from wall. I attempted to walk 
across room but was unable to do so. Most dreaded 
element was the sound — as though every nail in the 
building were being wrenched out at once. Damage 
moderate." 

932 Maltman Avenue (Silver Lake area, about 
one-half mile from southwest shore) . — Chimneys 
were cracked and overturned. Some plaster cracking 
was noted; window was cracked. Damage was slight 
to observer's home. 

4-fll Los Feliz Boulevard (south of Griffith Park) . 
— Chimneys were cracked, twisted, and overturned. 
"Older masonry buildings generally damaged. Dam- 
age was moderate." 

2835 Sunset Place (about 2 \/ 4 miles west by north 



ol ( i\ i< ' I Ik- ob* ■ ' 

in same hloc k fell; some cracked and will b' 

moved. Power lines in rear ol building flashing. 

There were reports ol broken dishes m the area. Wt 

live- in lour family flat (old wooden building). We 

had nothing broken one small mirroi fell." 

Hollywood area. Sidewalks were buckled. Win- 
dows were- broken. Chimneys < rai ked and fell, build- 
ings were damaged, especially brick buildings. The 
following accounts were received bom observers: 

"When we were awakened, it sounded as if a truck 
had hit the motel. It also felt as if the turn 
about to explode." "Aftei the earthquake, people 
were outside on sidewalks and would not go hack in- 
side because of the aftershocks. I thought the build- 
ing would disintegrate. Part of brick wall on roof 
fell. Arch ovei building entrance cracked, creating 
danger, brie k buildings seemed to be more damaged 
than single-structure cement buildings." At a.m., 
heavy earthquake, lor fust 'i or 3 seconds thought it 
would be the usual shake; then intensity increased 
suddenly. Thought all 'hell' was going to break loose. 
Bolted out of bed and stood under doorway. All 
thoughts blank except when would the she>ck end — 
seemed to last forever. Lights out almost immedi- 
ately and things overturned. Saw flashes of light from 
shorted telephone pole transformers — thought the 
whole city was ablaze. Got dressed and went outside, 
sat in car, as I thought there would be aftershocks. 
and there were. Went back inside about 45 minutes 
later; then went to work. Noted some traffic lights 
were inoperative. People went outside after the 
shock, then tried or attempted to go back inside, but 
aftershocks kept them outside for about 25 minutes. 
Cars were driven and parked irregularly." From ob- 
server at 1627 North Normandie Avenue: "Older 
brick buildings received the most damage. Chimneys 
cracked. Heavy objects moved. Water sloshed from 
toilet bowls. This area where I live was apparently 
jolted heavier than other sections of Hollywood. Per- 
haps adobe soil is responsible." "Chimneys fell at 
Hollywood-Wilshire area." "Husband had parked 
car at work. Saw lightning in sky and over moun- 
tains and heard loud rumble before shock. Car shook 
strongly, got out of car, earth moving up and down, 
got back in car. People were running out of houses. 
My husband drove back home and left for work 
later. At home, 519l/ 2 North Heliotrope Drive (near 
Los Angeles City College) , people were also fright- 



Felt Area and Intensity of Earthquake 



43 



ened and ran from houses. So many aftershocks, so 
close together, too many to count. Mostly sharp jerks 
on house, from east-west; some north-south shakes." 

5238 College View Avenue (south of Ventura 
Freeway and just southeast of southeast corner of 
Glendale city limits) . — Observer reported there was 
no damage to his 60-year-old, one-story home, but 
that most neighbors' chimneys were cracked, twisted, 
and overturned. 

5415 Wameda Avenue (Eagle Rock area). — 
"Damage considerable. Plaster fell. Furniture moved. 
Dishes Hew out of cupboards and shattered. Air-raid 
siren short circuited. Whole house shook violently — 
had to 'hold on.' My car fell off jack stands in garage." 

5151 State College Drive (California State Col- 
lege, just northeast of northeast Monterey Park city 
limits) . — "On the California State College campus, 
the new eight-story Administration Building is built 
on about seven pairs of reinforced concrete columns 
(no first floor) . Column pairs one and seven exhibit 
tension cracks. No other columns show any damage. 
Plaster cracks, 45° diagonal, only in east-west walls. 
Corners of rooms and steel doorframes show separa- 
tion cracks. Bookcases fell if facing east-west; gener- 
ally did not fall if facing north-south." 

3566 Lowry Road (in area about one-half mile 
southeast of Griffith Park, west of Golden State Free- 
way) . — "Chimneys on older homes cracked and over- 
turned. Considerable glass damage in vicinity. Many 
pre- 1933 masonry buildings severely damaged, some 
beyond repair, within a 2-mile radius of my house." 
(Also, 62 intensity VI and 101 intensity V reports 
were received from the Los Angeles area.) 

Montrose. — Chimneys and water tanks were 
cracked, twisted, and overturned. Ground was 
cracked. Water was disturbed. Plaster was cracked 
and broken. Windows were cracked. Damage was 
moderate. The press reported that powerlines were 
down. Damage was slight at 2261 Luana Lane, but 
chimney across the street was overturned. (One in- 
tensity V report was received from the area.) 

North Hollywood. — Water mains were broken. 
Chimneys fell. Large plate glass windows were bro- 
ken. Outdoor block walls were cracked and dislo- 
cated. File cabinet was overturned. The following is 
from an observer at 7262 Farmdale, about five blocks 
northwest of Hollywood-Burbank Airport: "I was 
awakened at 6 a.m. The house shook and rolled, and 



there were rumbling noises but not extremely loud. 
Climbing out of bed during the shaking, I was able 
to walk to my daughter's room. She was awake and 
was not terrified. Oven and refrigerator displaced 4 
inches. Flat steel plates (25 lb each) were moved on 
uncarpeted surface of floor. General disruption in all 
rooms. No readily observable cracks in ceilings or 
walls. Cement block wall in yard cracked at ce- 
mented joints, displacement about 1 inch. Immedi- 
ately after the shock subsided (lasted about 20 to 30 
seconds) , I checked lights and phone — they still 
worked. Water OK. I felt about five or six after- 
shocks between about 6:09 and 6:19 a.m.; then I sat 
down to record more aftershocks." This observer re- 
ported he felt 34 shocks to 1:30 p.m., with the 
strongest at 6:35, 6:44, 8:00, 8:30, 10:57, and 10:59 
a.m., and at 12:57 p.m. He stopped keeping record 
after 1:45 p.m. (Twelve reports of intensity VI and 
four reports of intensity V were received from the 
area.) 

Northridge. — Walls were cracked; chimneys were 
overturned; brick veneer was damaged. Exterior 
block walls were down. Windows were broken. The 
following is an excerpt from Lew et al. (1971) : 
"Northridge Hospital, Roscoe Boulevard near Re- 
seda. Five-story steel frame structure with reinforced 
brick masonry shear walls. The exterior cladding was 
of brick veneer. Damage to the veneer was extensive 
on the east and west elevations. The shear walls in 
the first story were badly cracked at many places. All 
mechanical and electrical equipment was functioning 
after the earthquake, including elevators." "The 
severe shaking seemed to last lor a period of about 2 
to 3 minutes. Multistory wood frame stucco buildings 
in neighborhood (9723 Rathburn Avenue) suffered 
extreme damage in shear walls but little damage in 
horizontal elements, such as floors and ceilings. Mod- 
ern reinforced masonry buildings all seem damaged 
around corners at roof level." At 10027 Wish Ave- 
nue, an observer reported: "Ground motion was very 
violent — seemed rippling — causing the house to tilt 
about 5°. Little or no structural damage or plaster 
cracking in the residences in our immediate vicinity. 
Considerable damage to concrete block walls in the 
area, particularly those oriented on an east-west axis. 
Approximately 100 feet of wall totally destroyed on 
my property. Floor lamps and table lamps were all 
tipped over; considerable breakage of dishes and 
bric-a-brac." At 10952 Etiwanda Avenue, near Chats- 



\\ 



Sail Fernando Earthquake <>\ 1971 



worth and Reseda, chimneys were cracked, twisted, 
and overturned. Pool watei was down 2 feet. Huge 
bookshelves were broken loose; five-drawei steel file 
cabinet was overturned. Damage was moderate. At 
8419 Yolanda Avenue, block wall was cracked; above- 
ground pool was damaged. Upright piano was 
moved 8 inches east; refrigerator was moved 3 feet 
southeast. Damage was slight. At 10106 Sylvia Ave- 
nue, block walls were topped and weakened; drive- 
way was cracked; portable planters were moved; tele- 
vision was overturned; bed was moved 6 ilK lies. 
Damage was slight. At I7 C >27 Burton Street, watei 
was disturbed and dirty. Electricity was off 30 min- 
utes; phone was out 2 hours. Trailer fell off jacks. 
Chest of drawers fell south. Movement was difficult. 
Many aftershocks were felt foi the first 2 days; sev- 
eral were felt thereafter. At 18822 Chase Sheet, patio 
cement was cracked and old cracks were widened. 
Chimney toppled next door. Block walls were weak- 
ened and ready to topple. Plaster was cracked. Watei 
cooler was broken; shower glass was cracked. No 
structural damage was noticed. At 19530 Pine Valley 
Avenue, chimneys were cracked, twisted, and over- 
turned in vicinity. YVrought-iron fence was broken. 
Plaster fell. Small overhang roof (tile) sagged and 
must be replaced. Damage was moderate. At 18098 
Kirkcolm Lane (in Porter Ranch district, about ?>\/ 2 
miles due west of Lower Van Norman Lake) , power 
was out. No water was available for 4 days. Exterior 
block walls were down. Windows were broken. 
Holes were found in stucco walls and doors. Plaster 
was cracked. Furniture was shifted. Cabinets were 
emptied. The following is from a report by California 
Institute of Technology (1971) : It was reported that 
$245,000 damage was sustained at the San Fernando 
State College, 18111 Nordhoff Street, and was due 
principally to collapsing bookshelves, toppling furni- 
ture, and falling glass from broken light fixtures and 
broken windows. "Only very minor cracking of 
structural members was found in the various build- 
ings on this campus, which included an eight-story 
dormitory and an eight-story office tower." (There 
were reports of eight intensity VI's and two intensity 
V's from the Northridge area.) 

Pacoima (excluding the more strongly shaken 
areas of northern Pacoima) . — Ground was cracked. 
Caslines were broken. Chimneys were overturned. 
Outside block walls were knocked down. Crack in 
floor the length of the building (post office) was re- 
ported. Furniture was overturned. Damage was mod- 



el. iw (Repon Irom postmaster. Post office located at 
Van Nuys Boulevard, neai J 'Kan Aven 
servei in the Arleta district, south ol Pacoima, in 
area just easi ol Panorama I "In our 

house the refrigeratoi opened and everything fell 
out, also most things fiom the- cupboards. Our ne-xt- 
dooi neighbor's cupboards face- the same direction as 
ours, with onl) a driveway separating the two ho 
hut she lost only 'die bottle of catsup. Our kitchen 
had to he < leaned OUI with a shovel. Most of the fur- 
niture in the family room moved al hast 6 to B 
inches Irom the walls, including a large pla\er piano. 
We couldn't tell in which direction it was shakr 
seemed to he both bouncing and swaying. We tried 
to walk through the house- to get the children and 
had to hold onto the walls to keep from falling. Our 
bloc k fences are all c lacked but still standing. We 
have many cracks outside, but few cracks inside. Fur- 
niture broken. Water disturbed. Plaster and win- 
dows cracked. Damage slight." (Two intensity VI re- 
[Kiits were re< eived from the area.) 

Panorama City — Building at 14545 Lanark Street 
was reported as being very badly damaged; also dam- 
aged was a building at #/'>'> Van Nuys Avenue 
(from a lettei h\ Superintendent of Buildings, De- 
partment of ( lounty 1- tigineer, Los Angeles i . "I he fol- 
lowing is an exc erpt from Few et al. (1971) : Kaiser 
Foundation Hospital, 13652 Cantata Street. Ten- 
story reinforced lightweight concrete shear-wall 
structure. There was severe cracking of the shear 
walls in the first, second, and third stories. The doors 
to the interior stairwell on the second and third 
floors were rendered inoperative due to the crushing 
of the spandrel beam in the shear wall. The fourth- 
floor slab, which is the transfer slab between the cir- 
cular tower shear walls and the walls below, cracked 
and displaced vertically. There was no apparent sign 
of structural damage above the fourth-floor level. 
About 50 glass panels fell from the building. All the 
elevators were out of service after the earthquake. 
The entire hospital remained in operation." Electric- 
ity was off over the entire area. At 14861 Lome 
Street, damage was reported as slight. Stucco cracks 
were noted; waterline was broken between meter 
and house. "Vertical motion of house was very pro- 
nounced, also lateral movement. Did not awaken 3- 
year-old girl." At another location, furniture was 
shifted; plaster was cracked. (Two reports of intensity 
VI and one report of intensity V were received from 
the area.) 



Felt Area and Intensity of Earthquake 45 



Pasadena. — At the Jet Propulsion Laboratory, 
4800 North Oakgrove Avenue, an estimated $200,000 
in minor damage to the Laboratory was reported by 
an engineer: "I arrived at work about 7:50 a.m. and 
made numerous surveys of buildings on the Labora- 
tory grounds to assess structural damage. Structural 
damage was superficial. Some spalling of concrete 
columns and concrete block walls. Some cracking of 
concrete walls. Considerable damage to architectural 
finishes (plaster, suspended ceilings, and lighting fix- 
tures) . Expansion joints and seismic joints had 
worked [out] and caused buckling of threshold strips 
and buckling and displacement of metal water stops 
at joints. Some waterlines broken." At the Millikan 
Library, California Institute of Technology, the fol- 
lowing damage was reported: "Nine-story reinforced 
concrete building. Many bookshelves collapsed on 
the upper floors and threw many books to the floor. 
With the exception of hairline cracking in the plas- 
ter around some window panels, no damage to the 
building itself was observed" (excerpt, California In- 
stitute of Technology 1971). Observers in several 
areas reported that chimneys were cracked, twisted, 
and overturned. Many windows were broken in busi- 
ness district. Cracking and fall of plaster were re- 
ported at a number of locations. Heavy sloshing of 
water from swimming pools was also reported. Ob- 
server at 1355 Daveric Drive (northeast Pasadena, 
north of Foothill Boulevard) reported that ground 
was cracked. The following statistics (Steinbrugge et 
al. 1971) do not include publicly owned structures: 
10 buildings damaged; four posted unsafe; buildings 
demolished or to be demolished include one church 
and one school; 2,000 chimneys damaged; and esti- 
mated total dollar loss at $2.5 million. Reports by 
Pasadena city officials roughly estimated damage at 
5200,000 to public property, with the majority of the 
loss attributed to road damage. The largest single 
item occurred on Park View Avenue, which runs 
parallel and east of Linda Vista Avenue. There, ap- 
proximately 800 feet of retaining wall, standing 11 
feet high, was affected, with approximately 300 feet 
of the wall reduced to rubble. Estimates for repair 
of the wall made up the major portion of the $200,- 
000 figure. (There were also 13 reports of intensity 
VI and 19 reports of intensity V received from the 
Pasadena area.) 

Reseda. — Block garden walls fell. Some roofs were 
buckled. Plaster cracked and fell. Heavy furniture 
was shifted and overturned. Water was sloshed 



from swimming pools. One observer stated: "Our 
fallen 6-foot block wall was not reinforced by steel. 
Stucco cracks were widened by aftershocks. Asphalt 
driveways cracked and some new sidewalk was 
cracked around power poles. Doors facing north or 
south on cupboards and on furniture flew open. 
Nothing fell from shelves running north-south, even 
from those near the ceiling. Windows in house are 
all aluminum framed and did not break, thousrh 
quite large. Some roofs in area buckled." (Five in- 
tensity VI reports and one intensity V report were re- 
ceived from the area.) 

Sepulveda. — At the Holiday Inn, corner of Roscoe 
Boulevard and Orion Avenue, the following was 
reported: "Seven-story reinforced concrete building. 
Extensive damage to interior plaster walls, to the 
plumbing fixtures, etc., on the second, third, and 
fourth floors. The upper three floors were not dam- 
aged severely. The nonstructural damage had been 
estimated at approximately $250,000" (excerpt, Cali- 
fornia Institute of Technology 1971). At the Veter- 
ans Administration Hospital (about 2.5 miles south 
of the Lower Van Norman Reservoir) , this report 
was received: "Buildings range from one to six sto- 
ries and are designed to resist earthquake forces. 
Overall, there was only minimal structural damage 
to the hospital. The operation of the hospital was 
not interrupted. However, extensive elevator and 
plaster repairs were required and a number of 
seismic joints required replacement" (excerpt, Lew 
et al. 1971). At 9037 Burnet Avenue, an observer 
commented: "Telephone pole tilted east-west (across 
street) . Chimney cracked vertically where it lies 
against house. Huge crack on cement foundation of 
q-aras^e floor, running east-west across floor. Small 
chicken shed tilted south. The house was a mess in- 
side. Anything on top of furniture (mantle, tables, 
etc.) was thrown down and broken. Stove and icebox 
moved in kitchen. In the garage, a 6- by 6-foot book- 
case, full of books, overturned. Garage had to be 
'dug through' to put things back in place. It suffered 
worse than the house. We inspected the house and 
did not see any new cracks, but since the aftershocks, 
we have found many new cracks, running south- 
north, about the thickness of a razor blade. There 
are many old cracks running in the same direction. 
All of our cement porches (three) have shifted 1 to 
one-half inch away from the house. We have found 
cracks outside both garage and house since the after- 
shocks. In our house, all objects on north-south walls 



46 



San Fernando Earthquake of 1971 



fell; in neighbor's house (across street), ;ill objects 
on theii easi west walls fell, none on north-south 
walls." At 10108 Gloria Avenue, 60 feel ol outside 
block wall fell and 150 feci was cracked; some inside 
and outside piasters ra< king was evident; damage was 
moderate. At 9752 Marklein Avenue, garden wall 
was ctacked; furniture shifted; stucco was slightly 
etackeel; ininoi kite hen-c ountci t lie c i ac king was no- 
ticed. "Earth motion was definitely north-south. 
Heavy hooks on north-south shelves fell sideways 
not off shelves. Portable television against north wall 
fell to door. Kitchen and both bathroom floors weie 
littered with broken glass. Hoi watei tank connec- 
tions loosened, water leaked. China cabinet and re- 
frigerator on east-west walls shilted (i inches from 
walls. No structural damage." Postmastei reported 
slight, nonstructural damage to post office; ground 
cracked, landslides occurred, and watei was dis- 
turbed; and chimneys, plaster, and windows were 
cracked. Other observers reported: "Water and gas 
service disturbed. Many windows e lacked in aiea, in- 
cluding a furniture store." "One-third e>l water emp- 
tied from swimming pool." "Slight spading ol side- 
walk at pool joints." (Three intensity VI reports 
were received from the area.) 

Sherman Oaks. — The Union Hank Building 
(northeast corner of Sepulveda and Ventura), a 13- 
story reinforced concrete structure, reportedly sus- 
tained some structural damage and considerable non- 
structural damage. "The structure is 13 stories high 
over a two-level subterranean garage. Structural dam- 
age was bunted principally to the four-corner col- 
umns." Nonstructural damage was reported as: "I le- 
vators out of commission; several doors in the 
second, third, fourth, and fifth floors were slightly 
jammed, indicating some partition movement; con- 
siderable areas of ceiling tile over the second floor 
fell; one drywall partition at the east end of the 
building buckled and showed horizontal movement; 
some steel stairlandings pulled away from their sup- 
ports but were still functional; five large panes of 
glass in the first floor cracked or broke; marble ve- 
neer in the first-floor lobby cracked and tell away 
from the walls and had to be replaced. The upper 
floors showed the least damage, and the penthouse 
showed no damage. The mechanical equipment in 
the penthouse was intact and securely mounted" (ex- 
cerpt, U.S. Geological Survey and the National 
Oceanic and Atmospheric Administration 1971). At 
the Bank of California Building (across the street 



Imjiii the Union Ban) Building; l2sioiv reinfj 
concrete structure), the following damage occurred: 
I I mi f- were i rai ks in the- building frame ovei most 

ol its height. 1 hese were espec iall\ protlOUfM ed in t!l« 

e ejiinec noil ol the- lightweight eonere-ie- beams to the 

noimal weight coiieieie- columns. This damage was 
being repaired with epoxy" (excerpt, Lev el aL 
l')7l). Observei at W/3 I Road reported I U- 

reinforced chimneys wen cracked, twisted, and • 
turned. Ground was cracked slightly. Piaster was 
cracked. Damage was slight. "Major ground motion 
appeared u> be cast west. I h<- major shock I 
about 60 seconds. Very little damage to hillside 

houses on lock in general vieiiiitv. Houses 00 sober 

substrata at lowei elevations appeared to sustain 
largei accelerations and damage. (There were six 
intensity VI reports and eight intensity V reports re- 
c eived from the area 

South Pasadena. Main chimneys were dam; 
and overturned. Large plate glass windows in several 
stoics weie bioken. Some old biick parapets fell in 
commercial area. One oi two buildings of unrein- 
forced masonry construction showed severe crack- 
in-. Ground c iae k was observed cur Monterey Road. 
Community water tower leaked. Water sloshed 6 feet 
on each side ol swimming pool. The following statis- 
tics (Steinbrugge et al. 1971) do not include- 
publicly owned structures: 20 buildings damaged; 1 
posted unsafe; 300 c himneys damaged; and estimated 
total dollar loss at $275,000. (In addition, there were 
seven intensity VI and lour intensity V reports re- 
ceived from the South Pasadena area.) 

Sunland.—At 8632 I.e Berthon Street (northwest 
Sunland area), observer reported: Block walls were 
thrown down. "Our heavy plate-glass mirror in bed- 
room was ripped off the wall, taking some plaster off 
the wall. Built-in oven was sprung from the cabinet. 
The hutch in dining room was thrown down, break- 
ing all contents, and landed on the dining room 
table; badly damaged." At 10734 Nassau, rocks in 
garden rolled. Damage to furniture and dishes was 
in excess of $900. At 10114 McBroom Street (west 
Sunland area) , furniture was shifted; glasses, food, 
etc., fell from cupboards, but no damage was re- 
ported. "Shock was violent enough to knock one off 
his feet if not holding onto something solid." At 
8442 Oswego Street, plaster, Avails, chimneys, and 
ground were cracked. Plaster and walls fell. Dishes, 
windows, and furniture were broken. Damage was 



Felt Area and Intensity of Earthquake 47 



slight to brick. (Two reports of intensity VI were re- 
ceived from the area.) 

Sun Valley. — Chimneys were cracked, twisted, and 
overturned. Outside reinforced concrete wall was 
cracked. Heavy furniture was moved east-west. Water 
in street was due to sloshing of swimming pools. "I 
was standing at the time; motion was a violent 
northwest-southeast shaking. Dining room fixture 
(4-ft chain) swung to the ceiling. Glass and crystal 
fell from every china closet in neighborhood." 
"Many people thought it was a bomb." (Reports of 
three intensity VI's and one intensity V were re- 
ceived from the area.) 

Tarzana. — At 18525 Linnet Street, house founda- 
tion was cracked. Waterpipe was broken. Plaster 
and windows were cracked. Toilet and bathtub line 
was damaged. Damage was moderate. "There are still 
(March 9) numerous strong aftershocks." Other ob- 
servers reported: Plaster cracked and fell. Cracks 
were widened in pavement and asphalt drives. Pool 
water was sloshed. (Two intensity VI and four in- 
tensity V reports were also received from the area.) 

Tujunga. — Ground was cracked. Minor cracking 
of pavement occurred. Chimneys were cracked, 
twisted, and overturned. Plaster and windows were 
cracked. Electrical wires were down. "Most of the 
dwellings in the area suffered only minor damage. 
Some older dwellings suffered moderate to major 
damage, but these were very few. Many commercial 
buildings had broken plate-glass windows. A few 
commercial buildings suffered moderate damage." 
Many aftershocks were felt. (There was one report 
each of intensities VI and V received from the area.) 

Van Nuys. — Ground was cracked. Chimneys were 
cracked, twisted, and overturned. Water was muddy 
for about 5 days. Outside block walls were cracked. 
Slab floor was cracked. Plaster was cracked. Heavy 
furniture was shifted. Pool water sloshed over top of 
house. "People here were very frightened, but kept 
control. In our general area, 8183 Lesner Avenue, 
west of Van Nuys Airport, near Balboa Boulevard, 
loss was mostly to dishes and personal items. Parts of 
block walls came down; water heaters moved, some 
off elevated stands, and most were inside houses in 
service porch area. Some people were thrown out of 
bed. Some cars rolled out of driveways or garages. 
Traffic became a major problem." (Reports of seven 
intensity VI's and 16 intensity V's were received 
from the area.) 



Verdugo City. — "Major damage to buildings in 
area. Many windows and dishes broke. Without lights 
until 10:20 and limited telephone service for most 
of the day." Plaster cracked. Small objects fell. Fur- 
niture shifted. Water sloshed from toilet. 

Vernon. — The following statistics (Steinbrugge et 
al. 1971) do not include publicly owned structures: 
30 buildings damaged; five posted unsafe; and esti- 
mated total dollar loss at $100,000. Postmaster re- 
ported there was no damage at the post office. 

Woodland Hills. — At 22233 Buenaventura, cement 
work, especially pool decking, was severely cracked. 
Tree was leaning. One-half of the pool water was 
sloshed out. Plaster was cracked. Furniture was over- 
turned. Damage was moderate. At 20513 Rhoda 
Street, few branches were broken off trees. Big tele- 
vision and stereo sets were moved a few inches. Ceil- 
ing, floor, and walls were cracked; more cracks were 
found in outside floor but not serious. Damage was 
slight. Other observers reported: Blocks in cement 
block fence were loosened; plaster was cracked; and 
pool water was sloshed out. "No electricity for 1 hour 
and 15 minutes. Electric power went out within sec- 
onds after start of shock. Gas and water supply re- 
mained OK. No telephone communication for 7 
hours." "Aftershocks seemed to be, in general, a 
rolling, wavy motion, causing a good shake. However, 
about one of four aftershocks seemed like a roll at 
first, then a big thud and dropping sensation. Per- 
sonally, I feel as if the ground and building were 
waving and moving all the time." (Also, there were 
five intensity VI reports and seven intensity V re- 
ports received from the Woodland Hills area.) 

REFERENCES 

Anonymous, "Oil Escapes Heavy Damage in California Quake," 
The Oil and Gas Journal, Vol. 69, No. 7, Tulsa, Okla., Feb. 
15, 1971, pp. 44-45. 

California Division of Mines and Geology, "The San Fer- 
nando Earthquake, 1971," California Geology, Vol. 24, 
Nos. 4-5, Sacramento, Apr-May 1971, pp. 57-96. 

California Institute of Technology, Earthquake Engineering 
Research Laboratory Report EERL 71-02, Pasadena, June 
1971, 512 pp. 

Lew, H.S., Leyendecker, E.V., and Dikkers, R.D., "Engineering 
Aspects of the 1971 San Fernando Earthquake," Building 
Science Series 40, National Bureau of Standards, U.S. De- 
partment of Commerce, Washington, D.C., Dec. 1971, 419 
pp. 

Los Angeles County Earthquake Commission, San Fernando 
Earthquake, February 9, 1971, County Board of Supervisors, 
Los Angeles, Calif., Nov. 1971, 45 pp. 



48 



San Fernando Earthquake of l n 7l 



Morrill, B.J., "Evidence ol Record Vertical Acceleration! at 
Kagel Canyon During 1 1 j « - Earthquake," The San Fernando, 
California, Earthquake of February 9, 1971, Geological Sur- 
vey Professional Papei 733, U.S Geological Survey and the 
National Oceanii and Vtmospherh Administration, U.S. 
Department <>l the Interioi and U.S. Department ol Com- 
merce, Washington, D.C., 1971, pp, 177 181. 

National Earthquake Information Center, Earthquake Infot 
mation Bulletin, Vol. 3, No, 2, National Ocean Survey, Na- 
tional Oceanii and Atmospheric Administration U.S. l)<- 
partment of Commerce, Rockville, Md., Mar.— Apr. 1971, 
27 pp. 



Si< inb kI V , Ichadi ill B IK and 

Ween, C.A., San Fernando Earthen 1971, 

Pacifu In' Rating Bureau, San Fran< ' if., 1971 9S pp. 

U.S Geological Survey and 1 1 < * - National Oceanu and At 
mospheri< Administration (Publishers), The Sun i 
California, Earthquake of February 9, 1971, '■ ' Sur- 

inal Papei 733, US. Department ol thi In 
and L'.S. Departmenl ol Commerce, Washington, l>(- 1971, 
2'>\ pp, 

Wood Han and Neumann, Frank, "Modified Mercalli 
Intensity S(.d< -,l I9S1," Bulletin of the Seismologieal So- 
nny of America, Vol 21, No. 1, 1»< I9SI pp - 



Focal Mechanism of 

San Fernando Earthquake 



CONTENTS 


Page 




49 


Abstract 


49 


Introduction 


64 


P-Wave Solutions 


65 


S-Wave and Combined Solutions 


66 


Conclusions 


67 


References 



W. H. DILLINGER 

Seismological Research Group 

Earth Sciences Laboratories 

Environmental Research Laboratories, NOAA 



ABSTRACT 

Body-wave focal plane solutions for the San Fer- 
nando earthquake of February 9, 1971, have been 
computed using long-period P-wave data and S- 
polarization angles, including solutions with com- 
bined P- and 5-wave data. The long- and short-period 
P-wave data give essentially the same result. The P- 
wave data reported to the National Earthquake In- 
formation Center (NEIC) give a solution that agrees 
well with data carefully read by the author. The 
NEIC-reported data do give a larger percent error, 
which is reflected in the larger error limits shown for 
this solution; however, the solution is good and 
demonstrates the feasibility of using reported P-wave 
data on a routine basis for earthquakes with M > 6.0. 

The best solution selected using combined P- and 
S-wave data for this earthquake gives one plane with 
strike N.65°W. dipping 55° to the northeast which 
is well determined, and a second plane with a strike 
N.40°W. dipping 37.7° to the southeast which is not 
as well determined. This solution gives excellent 
agreement with the observed field evidence found in 
the source region for horizontal compressional forces 
and the thrusting up of the San Gabriel Mountains. 

INTRODUCTION 

The San Fernando earthquake of February 9, 
1971, caused extensive damage in the Los Angeles 
and San Fernando areas. Many Federal agencies re- 
sponded to this earthquake by initiating studies of 
the effects. The Seismological Research Group of the 
Environmental Research Laboratories (ERL) sent a 
request to many cooperating stations around the 
world for use of their seismograms. Over 170 stations 
cooperated by loaning their seismograms. The com- 
plete set of seismograms was filmed by the Environ- 
mental Data Service (1971) . Copies can be obtained 



49 



r,0 



San Fernando Earthquake of 1971 



from the National Geophysical Data Centei ai Ashe- 
ville, N.C. 

Hypocenter parameters used in tin's study were re 
poiicd to NOAA by the California Institute ol 
I (( hnology as follows: 

Origin time: 14 00 41 6 GM I 
Epicenter: 34.4 N ., 118.4 W. 
Depth: 13 km. 

The body-wave magnitude m b reported by the Na- 
tional Earthquake Information Centei (Nl l< 
(i.2, and the surface-wave magnitude \I is 6.5. 
Even though there was extensive damage locally, this 
was only a moderate size earthquake in terms of 
source dimensions and radiated energy. Conse- 
quently, the S-wave motion was noi exceptionally 
well recorded at most ol the stations between dis- 
tances of 40° and 80°. This earthquake is on the 
lower limit for determining the orientation ol the 
focal mechanism from S wave data with i uncut tec h- 
niques. 

The P-wave first motion was also diffic ult to inter- 
pret at low-magnification stations where the signal- 
to-noise ratio was poor, such as some of the stations 
in Mexico and Central America, which might other- 
wise give important information on the focal mecha- 
nism of California earthquakes. The shallow depth 
of this earthquake, placing it in the upper crust, cer- 
tainly added to the complexity of both the P- and S- 
wave signals. 

Shortly after this earthquake, a preliminary solu- 
tion was computed by Dillinger and Espinosa 
(1971) using only P-wave data. This study uses addi- 



tional P-wave data, which were obtain* the 

deadline foi the previous report, hn> the study i 
marily improved b\ the use ol ^-polarization a: 
winch allow the determination ol an independent S- 
wave solution and ,i combined J' and S-wave volu- 
tion. 

One ol the- local planef ol tliis caithqn 

\ 65 \V. and dipping 55 to the nortl 
well determined b) P wave fust motions as shown in 
figure I. Using P-wave fust motions alone, du 
ond plane is determined verj poorly, having an al- 
lowable variation in stnkc of about 60" to 70 . The 
"combined maximum likelihood solution (solution 
No. I of table 1» shown in figure '. using the tech- 
niques developed h\ Dillingei et al. (1971), gives a 
solution loi the second plane with a strike of 
N.40 W. and dippin to the southeast. I 

results aie in good agreement with the P-wave fust 
motions. I he residuals foi the S-polarization angles 
are about 10 percent higher than would be allowed 
by the 95-percent fiducial limits ol the corresponding 
S-wave solution. As the magnitude of this earthquake 
is probably marginal for the use of S-waves, these 
high S-residuals were not considered too important, 
and solution No. 1 was considered "best" primarily 
because ol the better distribution ol P-wave data. 
This solution also gives good agreement with the ob- 
served geological evidence in the source regions, 
which indicates horizontal compressional forces and 
vertical uplift of the San Gabriel Mountains. 

An alternate possibility ('solution No. 2 of table 
1) shown in figure 6b, with one plane striking 



Table l.—San Fernando focal mechanism solutions 



Solution 



Pole of .4-plane Pole of P-plane 



Azimuth Dip Azimuth Dip 



N R, 



R. 



*.(95%) 


P-wave 
fidu- 
cial 
re- 


Rp 

fidu- 
cial 
bound- 




gion 


ary 




Percent 




10213.9 


96.4 


153 


2671.7 


97.8 


90 




98.7 


117 


3274.9 


98.3 


76 




99.3 


134 


5450.2 







Solution No. 1 : 

P-wave 10.00 

S-wave 195.00 

Combined 205 . 00 

Solution No. 2: 

P-wave 0.00 

S-wave 220.00 

Combined 215.00 

Solution No. 3: 

P-wave 5.00 

Solution No. 4: 

P-wave 10.00 

S-wave 190.00 

Combined 45.00 

Solution No. 5: 

P-wave 0.00 

Solution No. 6: 

S-wave 315.00 



40.00 


209.28 

328 . 22 

50.04 

192.96 
79.23 

74.23 

207.63 

212.63 
322.19 
205.72 

205.41 

200.85 


51.62 
27.99 
37.70 

50.73 

52.24 
52.24 

42.27 

42.27 
34.78 
51.62 

52.84 

33.23 


180 
20 

96 
18 

134 

91 

19 

149 
19 


155 

i54 
91 
91 

119 
79 
78 

136 






70.00 
55.00 

40.00 


6527 
11734 


7 

.1 


45.00 
45.00 

50.00 


1611 

1771 


4 

.3 


50.00 






65.00 
40.00 

40.00 


2037 
6712 


3 
.2 


75.00 


3390. 


5 



19.60 



10.37 



11.28 



14.56 



2.90 



1.82 0.00130 



.00465 



.00393 



Focal Mechanism of Earthquake 51 










bo 



San Fernando Earthquake of 1971 




r 












-= 
c 






Focal Mechanism of Earthquake 53 




•a 



60 

3 



o 

■a. 






< 



3 
to 



54 



San Fernando Earthquake <>\ I'Jll 



"?g 




"oo-oj r i OO'OOI 
,01 



00-08 0009 000» 00-02 OO'O 

sianoisaa jo S3«bnos jo uns 



■a 
- 




03 



oo-ooi 
,01 



00-08 00-09 00'0> 00-02 

si«nois3!j jo saaunos jo uns 



3 

to 



Focal Mechanism of Earthquake 55 



N.55°W. and dipping 45°NE. for the well-deter- 
mined plane and N.16.8°W. and dipping 52.2°SW. 
for the second plane, is also a good solution. This so- 
lution uses only what was considered to be the very 
best data. The long-period data were used for the F- 
wave observations; and the two S-polarization angles, 
which gave the highest residuals to the preceding so- 
lution, were discarded. 

One problem which occurred when looking at 
such a large number of original records was that, on 
a small percentage of the records, there was some 
question about the polarity of the instrument. A 
brief inspection of figures la and 8a shows several 
cases of inconsistent observations in the middle of 
many consistent observations nearby. While some of 
these may be errors in the readings, some were clear 
arrivals and even had records similar to nearby sta- 
tions, except they were reversed in phase. This prob- 
lem could be resolved easily if more attention would 
be paid by the station operators and managers to the 
polarity of their instruments, including making a 
clear indication on the record of the polarity. 

The fact that the worldwide station at Mexico 
City was not operational during this earthquake and 
that there is a lack of other high-quality data from 
the region in northern Mexico were real disadvan- 
tages. The occurrence of three dilatational obser- 
vations from Mexico (seen in the fourth quadrant of 
fig. la) gave the author the first impression that 
the second plane was well defined and dipping south. 
To resolve any focal plane which was dipping steeply 
southward for a southern California earthquake, 
some high-quality stations with long- and short- 
period instruments would be needed in Mexico. 

The data read by the author for this earthquake 
and the reported data are given in table 2 along with 
the distance, azimuth, and angle of departure for the 
F-wave. The azimuth is measured clockwise north 
through east, as are the azimuths given in table 1. 
The first motions listed under NEIC were those 
available to the Center by approximately March 1, 
1971. The first motions read by the author are fol- 
lowed by a relative quality factor: E = excellent; G 
= good; F = fair; and P = poor. All of the read- 
ings with the exception of those labeled poor are 
probably good enough not to be arbitrarily discarded 
without reinterpreting the record. The S-polarization 
angles were determined by digitizing the horizontal 
components of the long-period instruments and by 



plotting a particle motion diagram from which the 
polarization angle was measured. 

The computer procedure used for finding the best 
fitting focal planes is incremental. The orientation of 
focal planes giving the highest score determined 
from maximum likelihood is selected as the best so- 
lution. The P- and S-scores are combined with con- 
stants determined from maximum likelihood statis- 
tics to find the best combined solution. The fiducial 
limits for the P- and 5-wave solution are contoured 
on an equal-area projection of the focal sphere. For 
the S-wave solutions, the contours are 95-percent fidu- 
cial limits. The F-wave maximum likelihood surface 
is a step function because of the discrete nature of 
the data. Thus, it is seldom possible to contour an 
exact 95-percent limit because the score which is con- 
toured is the value which gives the next highest per- 
cent likelihood above 95 percent. A complete discus- 
sion of these techniques can be found in Dillinger et 
al. (1971). 

Several solutions were run to determine if 
different data sources would give significantly differ- 
ent answers. The computed results are given in table 
1. In each case, the solution given for the best F- 
wave solution is not unique. There is always a con- 
tinuous range over which the focal planes may be 
varied while keeping the same number of consistent 
observations of F-wave first motion. The F-wave so- 
lution printed in table 1 is the first solution found 
by the computer which has a score equal to the best 
score found. For the more important solutions, con- 
toured limits on the allowable variation of the F- 
wave solution are presented. From these diagrams, it 
is easy to see the range in orientation possible for the 
F-wave nodal planes. 

The contours shown on illustrations of F-wave so- 
lutions (figs, lb, 5b, 7b, 8b, and 9b) have two levels. 
The outer contour is of the fiducial limit. The per- 
cent likelihood contained within the fiducial limit 
for each solution is given in table 1. The inner con- 
tours closest to the given solution are the limits over 
which the pole can vary and still have the same 
value as the given solution, that is, the same number 
of agreeing and disagreeing observations. 

The contours presented for the combined solu- 
tions in figures 3b, 6a, and 9b are not computed fidu- 
cial limits of a known percent likelihood as is pre- 
sented for the individual F- and 5-wave solutions. 
However, as with fiducial limits, they are equal like- 
lihood boundaries and are contoured at equal incre- 



fjf) San Fernando Earthquake of I'Jll 



Table 2.—Ob$erved iim<i foi s«,i //,„,;,„/„ earthq 



Station 






■ of motioi 


i' 


■S'-v. 

polarization 


Amplitui 


1 






i 
























M* 


SP 


NEIC 




A, 






f l< atlOB 




i 


















mm 


mm 












AAK 


,. C 


1 


C 


G 














1 II 7 




4 


ADK 


... C 


(; 


c 


E 


' 












44 7 


311 




All 












- r ,\ 5 










69 B 


6 1 




ALB 






1) 


l 














15 6 


•- 2 


Vi : 


ALE 


. .. c 


(; 


c 


i; 


1 


-177 


1 1 


38 


B B 


3900 


',\ 8 


■<; 


20 4 


AM 






c 


(; 
















44 1 




ALQ 


c 


(; 


1) 


P 


C 




1 ,5 


9 


12 4 


175 


9 B 


83 4 




ANP 










c 


















AIM' 






c 


G 
















22 


19 


AUIl 


... c 


E 


c 


l, 






3.2 


7 r , 


10 4 


1000 


91 B 






ARK 


... c 


I. 


c 


E 


c 


- 59 . 7 


5 'i 


14 I 




1 500 


67.4 


1 K) 6 


21 


ASP 










c 












117 1 


B 


2 


All I 










c 














29 r > 


\ r j 1 


All 


... c 


G 


c 


G 






10 


II 


12 


woo 


28 2 






Avp; 






c 


(, 




















BCN 






1) 


G 














1 1 


M) 4 




BEC 


... c 


K 








-H 5 


i i 


11 .0 


B 


\y?) 








BIIP 


... c 


(. 


c 


F 


c 


135.7 










43.7 


116.2 




BLA 


... c 


c; 


c 


(; 






6 


15 


1 ', 2 


1 500 


10 B 




i\ 


BLC 


... c 


G 


c 


G 


c 




8.5 


51 5 


8.8 


1800 




17.8 




BLG 










D 


















HMN 






D 
















6 1 


8 4 




BMO 


... D 


E 


D 


E 














10 5 


4 2 




BNG 






C 


G 


D 












124 1 


55 2 


0.4 


BNII 






C 




















29.4 


BNS 


... C 


G 


C 


G 






1.8 


4.8 


9.6 


1000 


82 5 


II ', 


17.7 


BRK 










c 












4.7 


119.1 




BRW 










c 












42.2 


342 1 


28 8 


BTY 










c 












2.8 






BUH 










c 












84.6 




17.0 


BUL 


... c 


G 


C 


G 














147.0 




5.4 


BUT 


... D 


P 


D 


F 














12.4 


19.2 


51.7 


CAR 


... C 


E 


C 


E 


c 


-23.0 


10. 


27.3 


12.8 


3000 




104 2 


20 


CHI 






C 


G 




















CLE 






C 


F 














29.8 




il 


CMP 










c 












94.1 


24.9 


15.6 


COL 


... C 


E 


C 


G 


c 




4.5 


13.0 


9.2 


1 500 


35.3 


B.8 


29.9 


COM 






C 


G 














29.7 


120.9 


31 


COP 


... C 


G 


C 


G 


c 




2.5 


6.5 


10.0 


1500 


81.0 




17.9 


COR 


... C 


G 


C 


P 


D 












10.9 


541 .1 


53.0 


CPO 


... C 


E 


c 


G 






14.0 


62.0 


17.3 


2200 


26.8 


78.0 




CPP 










c 












70.4 


137.1 


19.1 


CPX 










c 












3.2 


2 


56.1 


CSC 






c 
















30.8 


80.0 


31.0 


CUM 






D 


F 


c 












54.4 


102.1 


25.6 


DAL 


... D 


E 


C 


P 


c 




20.7 


87.5 


8.0 


1500 


18.1 


88.8 


47.7 


DBN 










c 












80.8 


31.4 


18.0 


DBQ 


... C 


E 


C 


E 






12.0 


12.5 


4.4 




23.1 


01 .2 


34.6 


DEN 


... D 


E 


D 


F 














11.9 


59.3 


52.2 


DUG 


... D 


E 


D 


E 


c 




95.0 


256.0 


32.0 


3000 


7.3 


35.9 


55.1 


EKO 






D 
















6.7 


17.2 


55.4 


ELK 


... D 


G 






D 












6.8 


20.6 


55.4 


EPT 


... C 


F 


D 


F 














10.3 


101.4 


53.4 


ESA 


... C 


G 


C 


G 


c 




.8 


1.6 


2.4 




96.1 


262.4 


15.4 


ESK 


... C 


G 


C 


G 




165.5 


2.5 


5.5 


10.0 


750 


74.9 


32.4 


19.8 


EUR 










c 












5.4 


20.2 


55.5 


FAY 






C 
















19.8 


78.2 


40.6 


FBC 


... C 


E 


C 


G 


c 




9.8 


33.5 


9.2 


2800 


42.2 


30.4 


28.8 


FCC 


... C 


E 


C 


G 






8.5 


43.0 


7.2 


4500 


29.2 


26.1 


32.0 


FFC 


... C 


E 


C 


G 






19.0 






4600 


23.4 


24.5 


34.6 


FHC 










c 












7.8 


326.9 


54.8 


FLO 


... C 


E 


C 


E 






15.2 


51.5 


13.2 


1500 


22.9 


70.7 


35.1 


FOR 


... C 


G 


C 


F 














35.5 


66.2 


29.8 


FSJ 


... C 


G 


c 


G 


c 




3.5 


59.0 


14.8 


3300 


20.5 


350.2 


37.5 


FUR 










D 












86.3 


31.1 


16.7 


GCA 






D 


P 


D 












6.1 


63.1 


55.8 


GDH 


... C 


G 


C 


G 




170.3 


4.2 


15.5 


9.2 


1500 


49.4 


25.1 


26.8 


GEO 


... C 








C 












33.3 


70.0 


30.7 


GLA 










C 












3.3 


113.2 


56.1 


GMA 






C 
















38.8 


329.6 


29.3 


GOL 


... D 


E 


D 


P 


D 




33.0 


65.0 


32.0 


1500 


11.7 


59.2 


52.5 


GRC 










C 












83.2 


35.8 


17.5 


GRF 


... D 


G 


C 


G 


C 




12.0 


37.0 


16.8 




85.1 


30.1 


17.0 


GSC 










D 












1.6 


54.6 


56.7 



See footnotes at end of table. 



Focal Mechanism of Earthquake 57 



Table 2.— Observed data jor San Fernando earthquake— Continued 



Station 



LP 



Sense of motion ' 5-wave Amplitude 2 Station 

polarization T 3 magni- 

NEIC Ai A 2 fication 



SP 



Angle of 
Distance Azimuth depar- 
ture 



GUA C E 

GWC 

HFS 

HHM D G 

HLW C F 

HNR C G 

HUA C G 

HVO 

IFR 

INK C G 

ISA 

JAS 

JCT C E 

JER C F 

JOL 

KBL C G 

KDC 

KEV C E 

KHC 

KIP C P 

KIR 

KJN G E 

KLG 

KNB D G 

KRL 

KTG C G 

LAC C G 

LAO 

LHC C E 

LIS 

LJU 

LMP 

LON D E 

LPA C G 

LPB C E 

LPS 

LPZ C E 

LWI C F 

MAL C E 

MAT C G 

MBC C E 

MCV 

MDC 

MDZ 

MEK 

MHC 

MIN 

MLF 

MMA 

MNT D F 

MNV D G 

MRG 

MUN 

MWC 

NEW D E 

NIL C G 

NNA C G 

NOL 

NOR G G 

NOU 

NRR 

NTI 

NUR C E 

OLC 

ORV 

OTT C E 

OXF 

OXM 

PAL G E 

PAS 

PBJ 

PEL C E 

PIM 

PKF 



C G 

C G 

D G 

C G 



C G 

C G 

D 

C E 



D 
C 

C 
C 
C 



C 

C 

c 
c 

D 

c 
c 

c 
c 



C G 

D G 

D G 

C G 

C G 

C G 

C E 



D P 

C F 

C G 

C E 



C F 
C F 



C G 



G F 



C G 



D G 
C G 
D G 



D 



C 

C 

c 

D 
D 



C 

c: 
C 



1) 



c 
c 



c 

D 
C 
C 
D 
C 
C 

C 
C 
D 
C 
D 
C 



C 

G 
C 

c 



D 
G 
C 



-175.2 



16.0 



164.8 



-121.6 



6.0 



174.6 



mm 


mm 


Seconds 




km 





O 


3.0 


7.0 


8.0 


750 


87.9 
34.9 
77.9 
14.3 
109.9 


284.9 
40.6 
22.3 
11.8 
27.8 


16.2 
30.0 
18.6 
50.1 
6.4 


5.0 


13.5 


16.8 


1500 


88.5 
61.7 
35.9 
87.9 


257.6 

130.6 

255.1 

50.2 


16.3 
23.4 
29.6 
16.2 


10.5 


29.0 


9.2 


3300 


35.0 
1.2 
3.9 


350.3 
356.5 
335.6 


30.0 
88.8 
56.1 


12.0 


57.0 


11.2 


1500 


16.2 

109.6 

2.8 

111.1 

32.7 


98.8 

23.7 

307.4 

353.4 

326.2 


48.3 
6.4 

56.5 
6.2 

30.6 


3.2 


9.5 


10.0 


1500 


73.1 
86.5 


11.9 
29.3 


20.0 
16.6 


1.0 


3.2 


12.0 


375 


37.1 
73.5 


260.1 
15.1 


29.4 
19.8 


6.0 


16.5 


8.0 


1500 


78.2 

130.1 

5.2 

84.4 


14.5 

256.5 

58.4 

32.0 


18.8 

6.4 

55.5 

17.0 


2.0 


6.0 


8.0 


750 


60.1 

1.6 

15.4 


22.7 
89.5 
33.2 


23.6 
56.7 
49.7 


14.4 


55.0 


12.4 


3000 


25.8 
82.1 
89.4 
67.7 
12.6 


48.2 

48.2 

30.7 

275.1 

349.2 


33.1 
17.7 
16.0 
21.5 
51.5 


1.5 


4.5 


8.8 


750 


89.2 


134.3 


16.1 


4.0 


12.0 


12.0 


1500 


69.6 

33.1 

69.6 

135.8 


128.1 

120.0 

128.1 

50.9 


20.8 

30.7 

20.9 

6.0 


4.5 


12.0 


8.4 


1500 


86.3 


47.4 


16.7 


10.0 


31.0 


10.0 


3000 


79.7 


307.2 


18.3 


15.8 


49.0 


8.8 


3900 


41.9 
3.0 
4.5 

40.9 

130.9 

4.0 

6.5 

27.6 
5.4 


359.7 

40.4 

321.7 

77.7 

262.9 

319.1 

337.6 

70.1 

97.1 


28.7 
56.5 
56.1 
28.7 
6.4 
56.1 
55.6 
32.1 
55.5 


11.0 


21.0 


24.8 




35.6 
4.0 

31.0 

134.7 

0.3 


58.2 
2.6 

68.9 
257.1 
121.1 


29.7 
56.4 
31.0 
6.3 
93.0 


14.0 


29.0 


16.4 


1500 


13.9 


3.5 


50.3 


2.8 


8.2 


12.0 


1500 


111.4 
60.7 
24.3 


349.6 

131.9 

92.6 


6.4 
23.4 
34.8 


2.6 


7.6 


9.2 


750 


57.9 

90.9 

5.3 

14.3 


9.8 
243.5 
347.7 

3.8 


23.9 
15.5 
55.5 
50.1 


5.0 


13.0 


9.6 


1500 


80.7 
5.1 
5.7 


17.5 
316.9 
335.1 


18.0 
55.5 
55.5 


5.0 


24.5 


12.0 


3200 


34.2 
23.9 
22.4 


58.3 

81.4 

127.4 


30.3 
34.6 
35.5 


5.5 


17.0 


16.0 




35.5 

0.3 

27.3 


65.9 
143.1 
125.2 


29.8 
93.0 
32.2 


3.5 


9.6 


8.0 


1500 


80.7 

21.8 

2.2 


141.0 
133.3 
312.5 


18.0 
36.0 
56.9 



See footnotes at end of table. 



58 San Fernanda Earthquake of I'Jll 



Table 2 ObmrveA 'i»t<i j<>< sun innando tartkqmakg—CtmtlmmM 



Sense "i motion ' .V-wavr Amplitude 2 Btal \j± v ■ 

Station p o la riz a t i on J ' rna^m- Distance Azimuc 

LP SP NEIC Ai Aj fi'dtion 

mm mm Seconds km " 

»''<M C 1.6 128.1 

PMG C P % g | 7 

PMR C (i C G 1.8 7.5 8.8 1000 |.7 

PNS C 69.2 128.2 21.0 

PNT C F l> P 14 9 SS6 I 49 • 

POO ' 126.1 34. 6 Z 

POU ' M.3 |7.i 

I'Kl I' 2.6 313.8 

PRU <• 80 2 10 7 

Fro C E C G -20.5 15.0 8 1500 810 ft 17 9 

QUI C JO B 124 1 

RAB G F CI 1.0 2.5 18 4 750 919 6.2 15 6 

RBA C G J.O 7.2 7.5 50.7 

RCD D G D G 2.8 4 2.4 1500 10 2 40 49 9 

REN D I 5.3 34" 

RES G E C G C -5.0 10.6 33.5 8.0 MOO 42.0 9 1 

HOI. C G I) (i 9 40.0 12.4 21 7 73.0 36 1 

SCB C E 1.9 o 2 740 31.6 61.0 31 

SCH C I- ' 40.9 43.8 28.7 

SDB C F C P 1.6 4.2 8 2 1500 132.7 78.1 

SEA ' 1 is.6 Ml 50.5 

SES D G C G ' 3.0 6.3 4.0 3500 16.9 16.4 47 6 

SFA C E C G < 3.0 12.5 12.0 1900 37.6 29 4 

SHA C G <: I 25.7 89.8 33 2 

SHK C G C G 4.0 10.5 8.4 1500 84 5 308 3 17 

SJG C E C G I 127.0 2 7 7.6 8.8 750 49.1 95.5 26.9 

SLD D 3.5 320.1 56 1 

SLL C G 77.5 22.3 18 8 

SLM C E CO 23.0 71.2 35 

SMN C 3.0 25.2 56.1 

SOD C F 75.2 13.3 19.6 

STJ C G C G C 150.0 4.2 10 2 8.4 950 49.9 53.8 26 6 

STR C C F 2.0 5.0 10.0 750 84 5 32.6 17.0 

SUD C E 30.7 55.5 31.0 

SYP C 1.3 276.4 56.7 

TAB C 106.4 12.5 6.4 

TAC C F 22.7 126.3 35.3 

TEN C 83.5 60.0 17.4 

TFO C E C E 6.7 14.1 2000 5.9 89.0 55.5 

TNP D 3.8 14.1 56.1 

TNS C G 83.6 31.1 17.3 

TOL G F C E C 4.0 13.2 12.8 1500 84 4 44.8 17.0 

TPH C 3.8 14.1 56.1 

TPM DG 23.0 126.8 34.6 

TRI C G C G C 4.0 11.5 10.0 3000 89.3 31.3 16.0 

TRN -50.8 56.9 100.3 24.9 

TRO C 71.7 14.5 20.5 

TRY C F 35.6 62.9 29.8 

TSK C E 7.5 17.6 8.8 78.6 306.1 18.8 

TUC C E C 7.5 38.0 11.2 1500 6.7 105.9 55.4 

TUL C E C G 19.5 80.2 9.6 1500 18.5 78.8 45.8 

TUM D F 13.1 346.2 50.8 

UBO D D D 9.2 47.3 54.0 

UCC C G C G 81.3 32.7 17.8 

UDD C G 77.9 22.4 18.6 

UKI C E 6.1 322.2 55.8 

UME C G C G 17.0 35.0 8.8 5500 76.8 17.5 19.0 

UPP G G C G C 8.0 16.0 10.0 1700 79.3 20.9 18.5 

USC D 0.4 167.1 93.0 

VAL C G C G -21.0 2.1 6.0 9.2 750 73.6 37.8 19.8 

VHM C G 25.9 126.1 33.1 

VIC D G DP 29.5 89.0 22.0 2500 14.6 346.6 49.9 

VKA C G 88.3 28.4 16.3 

WES C G C 37.4 63.4 29.4 

WSC C 33.2 69.7 30.7 

YKC C E C 6.5 30.0 16.0 2250 28.2 3.8 31.8 

1 LP = long period, SP = short period, NEIC = National Earthquake Information Center (NOAA), C = compressional, D = dilata- 
tional, E = excellent, F = fair, G = good, P = poor. 

2 Ai = Amplitude of first J 2 cycle on long-period record; A 2 = peak-to-peak amplitude of first full cycle on long-period record. 

3 T = Period of first cycle. 



Focal Mechanism of Earthquake 59 




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Focal Mechanism of Earthquake 61 




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Focal Mechanhm of Earthquake 63 










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merits down from the maximum likelihood solution. 
Because the pen cm likelihood contained within 
these- contours is not known, the relative si/e cannot 
be compared from one solution to another. I he pur- 
pose ol these contours is to show the trend <>| the 
likelihood surface in the v ie inilv ol die sol u lion 

P-WAVE SOLUTIONS 

The sources ol P-wave data are long- and short pe 
riod records read by the authoi and data reported to 
the NEIC. Several solutions were run to evaluate 
these various types ol data and to find il the) would 
produce similar results. As can he seen from the con- 
toured fiducial boundaries lot the various P-wave so- 
lutions, they have all produced very similai and com- 
patible icsulls. The short-pet iod and reported data 
(io contain a larger percent of error in the observa- 
tions, hut the fiducial limits aie smallei and the re- 
sults are in agreement with the long-period data. 

In the following discussion, the contoured bounda- 
ries of the fiducial limits arc- used to evaluate and 
interpret the various solutions. These boundaries arc- 
primarily a function of three things: the distribution 
of data, the cpiality ol the data, and the number of 
alternate possibilities which exist in the data. The 
distribution of the data is, ol course, important. 
Where there is a region of the local sphere with no 
observed data, the focal planes can vary continuously 
over this region without being restricted. Such a re- 
gion may be large or small, depending on the distri- 
bution of the data. If the data contained no error, 
there would only be one such region within which 
the planes could be located. However, because there 
is always some possibility of error, each region de- 
fined by the data has some probability of containing 
the solution. This probability, which is also the like- 
lihood, is computed from the probability of an ob- 
servation being correct; this latter probability is the 
number of correct observations in the maximum 
likelihood solution divided by the total number of 
observations. The probability of an observation 
being correct is given in table 1 for each P-wave so- 
lution. If this value is multiplied by 100, it becomes 
the percent of the data in agreement with the maxi- 
mum likelihood solution. 

The boundaries of the fiducial limits are found by 
contouring the number of aoreeino- observations on 
the focal sphere. The value to be contoured is deter- 
mined as follows. For each region on the focal sphere 



Which is sampled, the likelihood is computed I hen 
these likelihoods aie summed stamny with the value 

loi the maximum likelihood solution and moving 
down until the fust value than oi equal 

percent is found. Because the long-period data are 
\ei\ consistent, allowing only one additional station 
to he- iii enoi detei mines the liduc lal limit; hov. 

loi the reported data, three additional stations must 
be- considered in erroi before reaching the fiducial 
limit ol 98.3-percent likelihood. Thus, the contoured 
fiducial limits allow reasonable comparisons ol re- 
sults from high-quality data with data for which the 
quality may not be as good, but where distribution 

may be bcltei . 

The solution with the most consistent data set 
obtained using long-period data icad by the author 
('solution No. '1 ol table I) . 1 his solution - 
pen cm agreement, which is the type of result that 
one would expect horn long-period data all read by 
the same individual. However, the data distribution 
is such that the solution may lie in a broad region 
(figs. ">a and 5b) I hus. it is txjssible that there are 
not many observations near the nodal planes where a 
greatei amount ol erroi would be expected. 

Solution NO. 1 o| table 1 was obtained using the 
short-period data read by the author and supple- 
mented by the u-ported data. This is essentially a 
short-period solution, since it is doubtful that much 
repotted data would come from long-period instru- 
ments. If the reported observation disagreed with 
that of the authoi. then the reading of the author 
was used. The agreement was 86 percent for this so- 
lution, which is the lowest of those reported here. 
However, it can be seen from figure 1 that this solu- 
tion has the smallest fiducial limits ol those obtained 
from P-wave data. Also, by comparing figures lb and 
5b, we can see that the contours of the short-period 
limits overlap those of the long-period limits, giving 
a result which agrees with the long-period data. 
Thus, solution No. 1 might be considered the "best" 
in that it has smaller limits and is in agreement with 
the long-period observations. 

The two preceding cases describe the orientation 
of the focal mechanism of the San Fernando earth- 
quake, particularly when they are combined with the 
S-wave polarization angles for the combined maxi- 
mum likelihood solution. There are, however, some 
interesting observations which can be made from the 
other three P-wave cases presented. The short-period 
readings made by the author were used in solution 






Focal Mechanism of Earthquake 65 



No. 3, which is shown in figure 8. While more data 
are available in this case, the percent error is also 
greater, which causes the fiducial limits to become 
larger. This result was not expected, but with consid- 
eration it seems quite reasonable and builds confi- 
dence in the statistical analysis. 

It would be desirable to get a good solution which 
uses reliable data and restricts the variation of the 
nodal planes as much as possible. For this purpose, 
solution No. 5 was run. This included all the data 
read by the author, long and short period, with 
long-period observations used when the two were dif- 
ferent. The nodal planes are only slightly more re- 
stricted than for the long-period data (compare figs. 
5b and 9b) . Thus, it is only when reported data are 
used, as in solution No. 1, that the distribution of 
the observations is improved enough to improve the 
solution significantly. 

A very interesting result was found when only the 
data which had been reported to the NEIC by ap- 
proximately March 7, 1971, were used. This solution 
was run to evaluate the reported data and to see if it 
would produce results comparable to the data read 
by the author (see solution No. 4 of table 1) . The 
observations give 87-percent agreement, which is not 
far different from the 89 percent given by the short- 
period data read by the author. When comparing the 
limits on this solution shown in figure 7 with the 
long-period residts (fig. 5b) , we see that the accepta- 
ble regions overlap to a large extent. The reported 
data restrict fiducial limits in strike considerably, but 
allow the limits to spread out more in the dip. 
These reported data contain more close-in observa- 
tions that were reported to the NEIC, but for which 
there was no opportunity to look at the records. It is 
these close-in data which restrict the strike of the 
planes the most. The best solution found, using the 
data reported to the NEIC, falls within the limits of 
the long-period data; thus, it can be seen that re- 
ported data can produce good results compatible 
with the best available data and, when statistically 
produced fiducial limits are provided, it is easy to 
evaluate the strength and weakness of the results. 

S-WAVE AND COMBINED SOLUTIONS 

The S-wave observational data are different from 
the P-wave case in that S-polarization angles are a 
continuously varying function over the focal sphere, 
whereas the P-wave data change only at the nodal 



planes. This gives certain advantages in handling the 
S-wave solution. The maximum likelihood S-wave so- 
lution turns out to be a least-squares solution. This 
makes the statistical analysis easier, and the fiducial 
limits can be determined in much the same manner 
as in usual least-squares problems. The quantities 
computed and contoured are therefore the sum of 
squared residuals for the S-polarization angle. This 
also allows the calculation of the value for an exact 
95-percent fiducial limit, which cannot be done in 
the P-wave case. All of the S-wave solutions presented 
in table 1 contain the following: N, the number of 
observations used; a, the standard deviation of an 
observation; R s , the sum of squared residuals for the 
maximum likelihood solution, and the value of the 
contour for the 95-percent fiducial limit. 

The continuous nature of the S-polarization angles 
means that it should be possible to get a solution 
with fewer observations than in the P-wave case, and 
the data points need not be near the nodal planes. 
In practice, it turns out that S-polarization angles are 
not too sensitive to the orientation of the focal 
planes. This is easily seen from figure 4, which shows 
a profile of the error surface as one plane is held 
fixed while the other plane is rotated through 180°. 
The value plotted is the sum of squared residuals. 
The very broad nature of the minimum regions seen 
in these figures is characteristic of the S-wave error 
surface. These broad minima are probably due pri- 
marily to the difficulty of determining the polariza- 
tion angle accurately. Two things are worth noting 
in these figures. In figure 4a, which is for solution 
No. 1 and uses all 20 polarization angles, it is easy to 
see that there are two minima. These also are seen in 
the contours shown in figure 2b. Secondary minima 
of this type could cause problems for iterative tech- 
niques of finding the solution. The other interesting 
point is how much narrower the minimum shown in 
figure 4b becomes for solution No. 2 for which the 
observations, giving the two largest residuals, were 
discarded. 

The use of all 20 S-polarization angles shown in 
figure 2a gives a broad fiducial region, and the best 
S-wave solution in the "least-squares" sense does not 
agree with the P-wave solution. However, two sec- 
ondary minimum areas within the fiducial region are 
seen in figure 2b to be close to the fiducial limits of 
the P-solution. It is this section of the S-likelihood 
surface which is enhanced when combined with the 
P-data and causes the selection of the combined solu- 



66 



San Fernando Earthquake of 1971 



(ion shown in figure Sa. 'I his combined maximum 
likelihood solution is in agreement with the P-wave 
data. 

Two stations, AF1 and LPB, have very high lesid 
nals lor the S-wave and combined solutions, is can 
he seen in table 8 nndei solution No. I. Discarding 
these two observations produces S-wave solution No. 
2, shown in figure ha, which agrees to a much largei 
degree with the /'-wave solutions and the resulting 
combined solution. Removing these two observations 
also reduces the standard deviation significantly and 
gives the narrower minimum discussed previously. 
Two solutions were run to find the independent t I 
feet of AM and LPB. It was found that disc aiding 
either station will improve the standard deviation al- 
most as much as removing both. Although the con- 
toured fiducial regions are not shown, it was found 
that LPB does not change the character of the fiducial 
region much from that obtained with both stations 
removed. It does, however, enlarge the region. This 
is most likely due to LPB being in disagreement 
with nearby stations which "average out" its influ- 
ence. The effect of AFI is roughly seen by compar- 
ing figures 2b and 6a. Since LPB did not change 
figure 6a significantly, almost all of the difference in 
the shape of the fiducial regions between these two 
solutions is due to AFI. This observation probably 
has such a strong influence on the solution because it 
stands alone in the center of the opposite half of the 
focal sphere from the other data. 



I lie- resulting s wave solution using AH is not 
ceptable, as it is in complete disagreement with the 

c data However, it is \<i\ encouraging u 
that, when the combined solution is found using die 

/'-data also, the secondary minimum oi the S-likeli- 
hood sui lace js picked up and the lesult is in n 
tnenl With the- P-wave data 

A single-couple solution was made for this earth- 
quake, and the- results weie reasonably n/fti 
(Solution No. 6 of tabic- 1). I he standard deviation 
ol the single couple is not much greater than a dou- 
ble- couple solution using the same data, which can 
l>c- sec ii h\ comparing solution No. 6 with solution 
No. 1. I he s wave solution alone does not agree 
with the P-wave data; however, when combined with 
the /'-data, a good result is obtained which gives 
agreement with both sets ol data. 

CONCLUSIONS 

The procedures used have proved to be very satis- 
factory foi determining the combined P- and S-wave 
solution. The fiducial limits on the individual P- 
and S-wave solutions are seen to be very helpful in 
evaluating and comparing various solutions. In de- 
termining the combined solution, the P-wave data 
seem to lie dominant. This is probably due to the 
broad insensitive minimums which are shown in 
figure 4 for the S-wave data. When the most incon- 
sistent S-eibservations are removed, the minimum re- 



Table 3.—S-wai>e residuals (O—Ci 



Station Observed 
polarization 

AFI -51.5 

ALE -177.0 

ARE -59.7 

BEC -14.5 

BHP 135.7 

CAR -23.0 

ESK 165.5 

GDH 170.3 

KEV -175.2 

KJN -16.0 

KTG 164.8 

LPB -121.6 

MBC 6.0 

NOR 174.6 

PTO -20.5 

RES -5.0 

SJG 127.0 

STJ 150.0 

TRN -50.8 

VAL -21.0 

Note: O — C = observed minus computed. 



Solution 


Solution 


Solution 


Solution 


No. 


1 


No. 


2 


No. 


4 


No. 6 


.S-wave 


Combined 


.S-wave 


Combined 


.S-wave 


Combined 


.S-wave 


-3.6 


-68.7 






-4.6 


-59.2 


24.3 


-1.3 


-7.4 


4.2 


4.8 


2.4 


-6.4 


-5.1 


5.1 


-4.6 


0.2 


-8.7 


-15.2 


-29.1 


12.2 


36.9 


24.8 


17.7 


20.6 


28.4 


21.1 


19.4 


10.5 


7.2 


4.9 


4.6 


-9.7 


-5.2 


12.0 


34.5 


29.7 


25.6 


27.6 


17.8 


21.5 


28.1 


2.4 


-5.2 


-0.1 


2.1 


2.9 


-5.8 


-6.8 


3.4 


-7.7 


-4.8 


-2.8 


5.3 


-7.7 


-7.0 


2.7 


-0.9 


12.7 


13.7 


5.2 


-0.3 


-1.2 


-16.0 


-19.5 


-6.2 


-5.0 


-13.9 


-19.0 


-20.3 


-5.6 


-14.3 


-8.7 


-6.9 


-3.7 


-14.2 


-14.0 


-56.4 


-63.7 












-6.5 


-10.7 


5.3 


4.9 


-1.8 


-9.1 


-7.0 


-8.3 


-14.0 


-2.6 


-1.8 


-4.9 


-13.2 


-12.4 


7.1 


-0.3 


2.8 


5.5 


5.8 


-1.8 


-3.4 


-7.5 


-15.4 


-5.9 


-5.2 


-3.6 


-14.4 


-12.2 


3.1 


-3.8 


-9.4 


-7.0 


-11.2 


-10.0 


-7.6 


7.8 


-6.0 


-10.6 


-7.7 


5.1 


-7.9 


-9.5 


6.9 


1.4 


-2.7 


-0.4 


-8.2 


-5.8 


-1.3 


0.6 


-7.6 


-4.2 


-1.7 


0.4 


-8.5 


-9.7 



Focal Mechanism of Earthquake 67 



gions become narrower (fig. 4b) and the standard 
deviation of an S-wave polarization angle is reduced 
considerably. It would appear that for S-wave solu- 
tions to become independently reliable, the standard 
deviations of S-wave polarizations would have to be 
improved over current capabilities. Nonetheless, the 
most consistent of the S-wave data gives good agree- 
ment with the P-wave first motions even if the S- 
uave data are not very sensitive to the precise orien- 
tation of the focal planes. 

The P-wave data provide some interesting results 
in themselves. The long- and short-period data pro- 
vide essentially the same result for this earthquake; 
when reported observations are compared with the 
short-period data read by the author, they are seen to 
be almost as good. This indicates that reported data 
are certainly good enough to be used in computing 
P-wave solutions, especially if the results are pre- 
sented with statistically evaluated fiducial limits on 
the variation of the focal planes. 

The excellent agreement that was found between 
the long- and short-period data would appear to 
imply that there is no difference in the long- and 
short-period solutions. For some earthquakes in a 
few areas of the world, Akasche and Berckhemer 
(1970) show solutions which give decidedly different 
results from the long- and short-period data. An 
inspection of their plots shows that there can be no 
question of the difference if the data are reliable. 



The San Fernando earthquake indicates that this 
problem may not occur in southern California; how- 
ever, a study of the long- and short-period data for 
more earthquakes will be necessary to determine if 

this is always true. 



REFERENCES 

Akasche, B., and Berckhemer, H., "Focal Mechanism of Deep 
and Shallow Earthquakes as Derived From Short and Long 
Period Seismograms," Proceedings of the X Assembly of the 
European Seismological Commission (ESC), Leningrad, 3-11 
September 1968, Vol. II, Academy of Sciences of the USSR, 
Soviet Geophysical Committee, Moscow, 1970, pp. 334-357. 

Dillinger, William H., Pope, Allen J., and Harding, Samuel 
T., "The Determination of Focal Mechanisms Using P- and 
S-Wave Data," NO A A Technical Report NOS 44, National 
Ocean Survey, National Oceanic and Atmospheric Adminis- 
tration, U.S. Department of Commerce, Rockville, Md., 
July 1971, 56 pp. 

Dillinger, W., and Espinosa, A.F., "Preliminary Fault-Plane 
Solution for the San Fernando Earthquake," The San Fer- 
nando, California, Earthquake of February 9, 1971, Geo- 
logical Survey Professional Paper 733, U.S. Geological Survey 
and the National Oceanic and Atmospheric Administration, 
U.S. Department of the Interior and U.S. Department of 
Commerce, Washington, D.C., 1971, pp. 142-149. 

Environmental Data Service, "The February 9, 1971, Califor- 
nia Earthquake and Complete Set of Seismograms From 
More Than 170 Stations," National Geophysical Data Cen- 
ter, U.S. Department of Commerce, Asheville, N.C., 1971 
(microfilm) . 



Seismograms, S-Wave Spectra, and 
Source Parameters for Aftershocks of 
San Fernando Earthquake 



CONTENTS 


Page 




69 


Abstract 


69 


Introduction 


70 


Equipment and Sites 


71 


Data and Analysis 


77 


General Spectral Characteristics 


77 


Fitting the Spectra to a Model 


79 


Sources of Error 


79 


S-Wave Sample Length 


79 


Propagation-Path Effects 


79 


Uncertainties of Spectra 




Interpretation 


79 


Radiation Pattern, Scattering, and 




Focusing Effects 


80 


Estimate of Combined Errors 


80 


Analysis of Results 


119 


Conclusions 


120 


Acknowledgments 


120 


References 



BRIAN E. TUCKER 

Institute of Geophysics and Planetary 

Physics 
University of California, San Diego, Calif. 



JAMES N. BRUNE 

Scripps Institution of Oceanography 
La Jolla, Calif. 



ABSTRACT 

A high sample-rate, high dynamic-range digital- 
recording system was used to obtain broadband, high 
signal-to-noise ratio seismograms and 5-wave spectra 
of 167 aftershocks (M L ~ i/ 2 to 4]/ 2 ) of the February 
9, 1971, San Fernando earthquake. The character- 
istics of the spectra — a relatively constant amplitude 
at low frequencies, a well-defined corner frequency, 
and a high-frequency asymptote with a slope from 
— 1 to —3 on a log-log plot — apparently represent 
seismic source properties and have been interpreted 
using the Brune model, giving seismic moments of 
10 1K to 10- L> dyne-cm, source dimensions of 50 to 
500 m, and stress drops of 1 to 300 bars. An apparent 
upper limit in stress drop (more than an order of 
magnitude greater than stress drops previously re- 
ported for small earthquakes) may represent the 
regional effective stress, while the range in stress 
drops may correspond to a range in fractional stress 
drops. 

INTRODUCTION 

This paper presents seismograms and corrected 
S-wave spectra for 167 aftershocks of the February 9, 
1971, San Fernando earthquake. The Richter magni- 
tude of these aftershocks ranged from about \/ 2 to 
4y 2 . Except for eight events in December 1971, all 
events were recorded during the first 8 days follow- 
ing the main shock. This data set is more complete 
and more reliable than any similar set previously 
obtained for several reasons: (1) The corrections for 
propagation effects were small because the average 
hypocentral distance was short (12 km) and the 
propagation path was through granitic rock; (2) the 
records were made on well-calibrated, high sample- 
rate (150/sec), high dynamic-range (90-dB) digital 



69 



70 



San Fernando Earthquake <>\ 1971 



equipment; and (3) an estimate ol experimental 
errors could be made because ol the large numbei 
of events recorded and because ol the simultaneous 
recording ol 14 events al two different sues. 



EQUIPMENT AM) SITES 

A high sample-rate, high dynamic lange digital- 
recording system was necessary to obtain bioadband 
spectra with high signal-to-noise ratios. Two record- 
ing systems were operated, each consisting ol a 
Ranger seismometer, an amplifier, an analog -to- 
digital converter (A-D) , and a digital tape ie< order. 
The seismometer was operated in the horizontal 
mcxle with about 70-percent critical damping and a 
1-Hz natural frequency. The amplifier gain (25 to 
3,150) could be varied in (i-dli steps. During the first 



2 d.iys ol operation, the amplifiei was bypassed to 

avoid ( lipping on lai ntt. A ti 

R.C liliei between the amplifiei and the A I) was 

used (almost always) to reduce aliasing 1 he maxi- 
mum output ol the A J) was •- 16,384 "counts," 

which corresponds to an input of - 10 volts. I he. 

output ol the A I) was recorded 150 times a second; 
hence, the \\cjuist frequency ('one-half the sampling 
rate; was 75 U/ 

The system was calibrated in five independent 
ways: (1) lilting a known weight from the seismom- 
eter mass; (2) using a well-calibrated shake table; 
' ''. measuring the- seismometer's coil constant; (4) 
using a Wilhiioic- budge: and (5) driving the seis- 
mometer, using its calibration cod, and optically 
measuring the motion of the mass. The resulting re- 
sponse (curve- I, fig. 1) is estimated to have an accu- 



o 

CO- 
CO 
UJ 

cr. 

O 



-2 



— ' 2 

— ■ ~ 

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Figure 1. — The basic recording system — a horizontal, approximately 0.7 critically damped Ranger seismometer (1-Hz natural frequency), 
an amplifier, an analog-to-digital converter (A-D) and a digital tape-recorder — was calibrated to an estimated accuracy of ± 6 per- 
cent by means of five essentially independent methods, mentioned in the text. The resulting response (curve 1) was used to calculate 
the response of the system including a two-stage, loit'-pass RC filter (between the amplifier and A-Di with cutoff frequency 60 
(curve 2) and 50 Hz (curve 3) while the response of the basic system excluding the amplifier (curve 4 ) was obtained from a separate 
calibration experiment. The amplifier's internal filters and the damping effect of the amplifier's input impedance on the seismometer 
cause the difference in shape of curves 1 and 4 for frequencies less than 2 Hz. Response units are A-D output (counts) per input 
ground motion (microns). 






Source Parameters for Aftershocks 71 



racy of ±6 percent. The response with the low-pass 
filter (curve 2 for 60-Hz cutoff frequency; curve 3 
for 50-Hz cutoff frequency) was calculated from 
curve 1. The response of the system with the ampli- 
fier bypassed (curve 4) was obtained from a separate 
calibration experiment. The amplifier's internal fil- 
ters and the damping effect of the amplifier's input 
impedance on the seismometer cause the difference 
in shape of curves 1 and 4 for frequencies less than 2 
Hz. 

To minimize propagation effects, the two record- 
ine sites — Bear Divide and Dillon Ranch — were lo- 
cated on granite outcroppings close to the epicenters 
(fig. 2) . The hypocentral distances ranged from 3 to 
28 km. 



DATA AND ANALYSIS 

The data tapes were computer-searched for signals 
exceeding a certain threshold. Selected signals were 
copied onto a composite tape and plotted. Noise 
bursts, electronic artifacts, and earthquake signals 
unusable because of either poor signal-to-noise ratio 
or electronic saturation were excluded. This left 220 
seismograms for 167 earthquakes — 27 of the earth- 
quakes were recorded on two orthogonal horizontal 
seismometers located at the same site, and 25 were 
recorded at both the Bear Divide and Dillon Ranch 
sites. The California Institute of Technology 
(C.I.T.) and the U.S. Geological Survey (USGS) 
determined the epicenters (fig. 2) and depths of 91 
of these events. 



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Figure 2.— Map of San Fernando area with locations of several well-known landmarks, our two recording sites, and the epicenters 
(obtained from C.I.T. and USGS) of the main event and 91 aftershocks studied in this paper. 



72 



San Fernando Earthquake of l'J7l 



Two hundred and twenty seismograms and theii 
corrected S-wave spectra are presented in figure 5. 
Scales for time, logi (frequency), and relative log M 
(amplitude spectrum) are given on each page. Each 
seismogram-spectrum paii has been given an identifi 
cation number. Those events recorded on two instru- 
ments have two seismogram-spectrum pahs, each 
with the same identification number. Foi events re- 
corded at both Heat Divide and Dillon Ranch, the 
numbers are followed by B 01 D, respectively, to 
specify the site; foi events recorded on orthogonal 
instruments located ai the same site, the subscript 
E-W or N s specifics the component ol ground mo 
lion recorded. For events numbered 1-22, E-W 
means W.37°S. and N-S means N.37 W.; otherwise, 
E-W and N-S mean true east-wesi and true north 
south, respe< tively. 

Table 1 summarizes pertineni information lor 216 
of the seismogram-spectrum pairs in figure 5. Using 
the notation described above, the recording site and 
component of motion recorded are indicated in the 
Site and Orientation columns, respectively. The 
more accurate origin times (those given to the- near- 
est second) were obtained from C.I.T. and USGS 
The hypocentral distances were calculated from the 
S—P times, using a /'-wave velocity ol 6.0 and a S- 
wave velocity of 3.5 km/sec. When the P-wave arrival 
time is uncertain, the corresponding distance esti- 
mate is in parentheses. For determining the absolute 
amplitude of each seismogram, the column Range 
gives the difference (in counts) between the maxi- 
mum positive and negative amplitudes, the Response 
curve column identifies the appropriate curve in fig- 
ure 1, and the column Attenuation specifies the 
amplifier's attenuation (in decibels) relative to that 
curve. Blank spaces are equivalent to ditto marks; 
therefore, the fifth row reads, from left to right: 
5, N-S, D, 2/10/71, 1131 34, 8. 13, etc. 

To obtain each S-wave spectrum in figure 5, we 
calculated a Fourier transform of that part of the 
seismogram underlined. A typical S-wave sample was 
about 1.5 seconds long (225 data points) ; its begin- 
ning and ending were chosen so that the numerical 
values of the first and last data points were close to 
the zero-level of the signal immediately preceding the 
P-wave. This zero-level was subtracted from the 
numerical value of each point of the sample. The 
points preceding the sample were set to zero, and 
other zero points were added to the end of the sample 
to make each time-series 1,536 data points long (for 



computational ease). Jim series <x k = 0, 1, 
N — \) was transformed usm^ a ( 
Fast-Fouriei fransform program which calculated 



exp(-f 





'■ 1. 2 V-l. 

I he- amplitude- spec Hum was obtained by correct- 
ing lo) instrument response and propagation-path 
attenuation. With A' equal to 1,556 and a Nvcjuist 

flCCjUCIIC v ol 7"> I f/, 




;-0, 1, ... 768, 
where <.> . A , and 1. are, respectively, the values of 
amplitude spectrum, Suave Fouriei transform, and 
instrument response at frequency (7 768) ~~> H/, 

propagation-path attenuation is compensated for by 
the exponential factor, where R is the hypocentral 
distance (in km), (i is the S-wave velocity (3.5 km/ 
sec 1 , and Q is the quality factor (250) . For one of 
the two spectra calculated lor event 73 in figu 
the individual values ol Q are plotted separately in 
the othei spectra, the values are connected by 
straight lines. The minimum frequency of each spec- 
trum is the reciprocal of the length of the S-wave 
sample; the maximum frequency is 75 Hz. 

Occasionally, events recorded at the same site on 
the same instrument component have spectra that 
are remarkably alike in detail. Seven pairs of events 
having such spectra are: 27. 28; 30, 77: 62, 63; 118, 
119; 125, 127; 129, 130; and 133, 134. The likeness 
is most pronounced between 1 and 10 Hz and can 
be seen by overlaying comparable spectra on a light- 
table. Similarities may result from like-scattering 
effects because, in every case where similar events 
have been located, their hypocenters are identical 
(within experimental errors) and because spectra of 
the same earthquake recorded at different sites are 
not similar. Two spectra obtained from recordings 
of an event on orthogonal seismometers at the same 
site typically do not show strong similarity, although 
they share general characteristics. In fact, there is 
often a striking difference in the appearance of 
seismograms of an earthquake recorded either at 
different sites or on orthogonal components located 
at the same site; for example, compare the two 
seismograms of event 6 (orthogonal components at 



Source Parameters for Aftershocks 73 



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Source Parameters for Aftershocks 75 



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Source Parameters for Aftershocks 77 



the same site) or those of event 146 (different sites) . 
From the Range column in table 1, it is seen that 
the peak-to-peak amplitude of the seismograms 6N-S 
and 6E-W are 3,796 and 1,449, respectively, while 
those of seismograms 146B and 146D are 708 and 
367, respectively (the instruments had the same 
response and attenuation) . Thus, the difference in 
the appearance of the seismograms is caused primarily 
by the large spike at the beginning of the S-waves in 
6N-S and 146B. 

GENERAL SPECTRAL CHARACTERISTICS 

Figure 3 illustrates the general characteristics of the 
spectra in figure 5. All plots are log-log and have 
been shifted vertically for clarity; slopes are indi- 
cated. Figure 3a is the response of the recording sys- 
tem to ground velocity. The bold line in 3b is a 
hypothetical input velocity spectrum of the S-wave 
of a signal that has traveled 12 km through a medium 
with a Q of 250. The dashed line in 3b represents 
the spectrum of the same signal traveling through a 
medium with infinite Q. The dashed line merges 
with the bold line at low frequencies. The spectrum 
of the hypothetical background noise is indicated by 
the thin line. The shape and relative levels of these 
hypothetical signal and noise spectra are typical of 
observed spectra. For frequencies less than f x and 
greater than f 2 , the noise level exceeds the signal 
level, whereas between fj and f 2 , the input is pre- 
dominantly signal. The actual spectrum of the seis- 
mometer output was obtained by multiplying the 
response curve 3a by the input (signal plus noise) 
spectrum 3b and is represented by the dotted line in 
3c. The solid line in 3c represents the spectrum calcu- 
lated from a discretely sampled section of the S-wave. 
The lowest frequency, f L , equals the reciprocal of the 
length of the S-wave section; and the highest (Ny- 
quist) frequency, f N , equals one-half the sampling 
rate. The solid line coincides with the dotted line 
except for frequencies greater than about f 2 where 
aliasing errors cause the calculated spectrum to ex- 
ceed slightly the actual spectrum. The dashed line of 
3c represents the calculated spectrum after correcting 
for propagation-path attenuation. The apparent in- 
put velocity spectrum 3d is obtained by dividing the 
corrected output spectrum (dashed line in 3c) by the 
response curve 3a. The solid line in 3d and the 
dashed line in 3b are identical except for frequencies 
greater than f 2 or less than i lt where 3d is greater 



because it is predominantly noise that has been arti- 
ficially corrected for attenuation over a 12-km path. 
The hypothetical amplitude spectrum 3e was ob- 
tained by dividing 3d by frequency; it has character- 
istics similar to those of the observed spectra (fig. 5) . 
In the absence of noise, this hypothetical spectrum 
would have a constant amplitude for frequencies 
from zero to the "corner" frequency (f c ) and a slope 
of —2 for higher frequencies. In the presence of 
noise, it has a negative slope for frequencies less than 
fi and a positive one for frequencies greater than f 2 . 
The values of fi and f 2 depend on the signal-to-noise 
ratio and, indirectly, on f c . The rate of increase of the 
spectrum above f> depends on the hypocentral dis- 
tance because this part of the spectrum is pre- 
dominantly noise that has been multiplied by an 
exponential factor to compensate for attenuation over 
this distance. 

FITTING THE SPECTRA TO A MODEL 

The spectra shown in figure 5 characteristically 
have a constant amplitude at low frequencies, a 
corner frequency, and a high-frequency asymptote 
with slope from —1 to —3. Deviations from this 
general character almost always can be attributed to 
noise. We have ignored the narrow minima that 
occur throughout the spectra, assuming they are the 
result of phase interference that we are not attempt- 
ing to interpret. Such phase interference could be 
caused by complexities in the source, scattering, or 
reflection. 

To determine the effect of background noise on a 
particular spectrum, a sample of the record (equal 
in length to the S-wave sample and, typically, 
immediately preceding the event) was Fourier- 
transformed and corrected for attenuation in the 
same way as was the S-wave spectrum. In general, 
the effect of the noise on the S-wave spectra is as 
shown in figure 3. When noise exceeds signal at low 
frequencies, the slope of the spectrum is negative; 
and when the noise exceeds signal at high fre- 
quencies, the slope increases at a rate proportional to 
hypocentral distance. Contamination of the S-wave 
spectra by P-wave energy was insignificant. Events 
with clipped seismograms (indicated by a " (c) " be- 
low their identification numbers in fig. 5) , had 
anomalous spectra at high frequencies (e.g., 28 E-W, 
102, HOB, and HOD). Several of the spectra of 
events recorded at Dillon Ranch on February 14 and 



78 San Fernando Earthquake <>j 1971 

15, 1971, have a peak (ai about 38 Hz) that is not 149). They ma) have been caused bj resonance of 

present in the associated noise spectra. These peaks nearby trees oi buildings. 

were considered anomalous because they are narrow- \ <ui\<- with a constant low-frequency atnplii 

band and missing in spectra foi the same earthquakes and a variable high-frequency sloj><- was fit to £16 

recorded at Bear Divide (e.g., 138, H4, 146, and spectra (pi 165 aftershocks) in figure 5 the reauHH- 



LOG 

VELOCITY 

RESPONSE 

(counts/ii) 



LOG 

ACTUAL VELOCITY 

SPECTRUM 

(u/cps) 




LOG 

APPARENT VELOCITY 

SPECTRUM 

(u/cps) 



LOG 

APPARENT AMPLITUDE 

SPECTRUM 

(u/cps) 



FREQUENCY (cps) 

Figure 3. — Illustration of the effect of background noise and propagation-path attenuation on amplitude spectra. All plots are log 
(frequency) versus relative logarithmic units of response or of spectral density (u = ground amplitude, u = ground velocity, 
"counts" = output of recording swtcm): slopes are indicated on each plot. The input S-wave velocity spectrum of an attenuated 
(Q = 250, hypocentral distance = 12 km) signal (bold line in b) merges at low frequencies with that of an unattenuated signal 
(dashed line in b). The hypothetical, but typical, signal and noise (thin line in b) spectra are equal at frequencies f ] and f f . The 
actual spectrum of the recording system output (dotted line in c) is obtained by multiplying the recording system response (a) by 
the hypothetical input spectrum (sum of the solid lines in b). The spectrum of a discretely sampled section of the S-wave (solid line 
in c) begins at f L (the reciprocal of the length of the S-wave section) and ends at / v (the Xyquist frequency I; collection for atten- 
uation (dashed line in c) and system response give the apparent velocity spectrum (d). The combined effect of noise and attenuation 
on the corresponding amplitude spectrum (e) — a negative slope below fi and a slope which increases at a rate proportional to hypo- 
central distance above f* — can be seen in the observed spectra (fig. 5). 



Source Parameters for Aftershocks 79 



ing four spectra (3, 11N-S, 140B, and HOD) were 
not interpreted because their general shape was not 
well approximated by such a curve. The fit was per- 
formed by adjusting the curve's low-frequency ampli- 
tude (fio) , corner frequency (f c ) , and high-frequency 
slope to average the amplitude (not log amplitude) 
of the spectra. Allowance was made for the fact that 
the density of spectral estimates, (Q;) , increases with 
log (frequency) , and therefore the character of the 
spectra between 10 and 20 Hz, for example, is more 
reliably determined than that between 1 and 2 Hz. 
Those parts of the spectra judged to be noise were 
ignored. Results of this process are indicated by the 
dashed lines on the spectra in figure 5 and by the 
values of Q , f,., and slope in table 1. 

SOURCES OF ERROR 

S-Wave Sample Length 

The level and shape of the spectra do not depend 
critically on the length of the S-wave sample, pro- 
vided the frequencies of interest are greater than the 
reciprocal of the sample length. This fact is illus- 
trated by comparing the spectra of two samples, of 
different length, of the .S'-wave of event 73 (fig. 5) . 
The arrowheads under the seismoeram indicate the 
endings of the two samples; the longer sample in- 
cludes the shorter. The spectrum of the longer is 
plotted as individual points and that of the shorter 
as a continuous curve. It is seen that the dashed curve 
fits both spectra equally well. Many such comparisons 
have been made with similar results. 

Propagation-Path Effects 

Our correction for propagation-path attenuation 
affects the spectra most strongly at high frequencies 
(fig. 3c) . Therefore, if our choice of Q (250) were 
grossly in error or if scattering were seriously affect- 
ing our data, we would expect a marked dependence 
of corner frequency and of slope of the spectrum at 
high frequencies on hypocentral distance. As a check, 
the corner frequency and high-frequency slope of 
each of the 216 spectra in table 1 were plotted 
against distance. The spectra were considered collec- 
tively and in groups with comparable Q 's; no corre- 
lation was found. 

Although the effect of near-site attenuation or scat- 
tering would be independent of hypocentral 
distance, it seems improbable that such attenuation 
and scattering alone could explain the wide range of 



corner frequencies observed. We found no significant 
dependence of corner frequency on the hypocenter's 
geographical location or depth. Thus, circumstan- 
tial evidence suggests that the observed corner fre- 
quencies and high-frequency slopes are not a result 
of propagation-path effects. 

Uncertainties of Spectra Interpretation 

Examination of the spectra and dashed lines in 
figure 5 shows that, in some cases, there is consider- 
able uncertainty in the choice of Q , fc, and slope. 
For example, by fitting a spectrum with a steeper 
high-frequency slope, one often can increase corner 
frequency. Some spectra seem to have two corner 
frequencies (e.g., event 25N— S at 4 and 20 Hz, event 
57 at 8 and 20 Hz, event 58 at 10 and 40 Hz, and 
events 96E-W and 96N-S at 6 and 15 Hz) . Except 
in the few cases (like events 58 and 25N-S) where 
the ratio of the two corner frequencies is large 
(>4) and the smaller value was used, the spectra 
were interpreted with an intermediate corner fre- 
quency. In general, interpretations of the spectra 
with steep slopes (— 3) and/or high signal-to-noise 
ratios (100 to 1,000 at f c ) are less ambiguous than 
those of the spectra with shallow slopes (— 1) 
and/or low signal-to-noise ratios (<20 at f c ) . The 
ambiguity of the fit of each spectra has been esti- 
mated and is indicated in the Quality column in 
table 1. The least ambiguous interpretations have a 
quality of 3, the most ambiguous a quality of 1, and 
the average a quality of 2. When a seismogram is 
clipped, the associated quality estimate is in paren- 
theses. 

An upper limit for the errors in Q and f c , resulting 
from ambiguity in interpretation, was estimated by 
making two alternate interpretations of 59 of the 
most ambiguous spectra. For each pair of alternate 
interpretations, we calculated the variance of the 
interpretations from their mean. The average of these 
59 determinations of variance corresponds to a stand- 
ard deviation in fi or f c of about 75 percent. The 
standard deviation for the other 157 less ambiguous 
spectra was estimated to be 10 percent. A weighted 
average of the two corresponding variances indicates 
that the standard deviation in Q or f c resulting from 
ambiguities in the fitting procedure is 25 percent. 

Radiation Pattern, Scattering, and Focusing Effects 

Because we recorded at only one or two stations, it 
was impossible to average the spectra over azimuth 



80 



San Fernando Earthquake of l'J7l 



.iihI thereby to eliminate 1 1 » * - effet is ol radiation pal or I. ;is a result ol ; * 1 1 errors is aboul 50 pen ent I his 

tern, scattering, and focusing. To a certain extent, may somewhat underestimate the total errors b» 

this difficulty was overcome by recording a large num in man) <asc-s, the two sites did not sample 

ber ol events a) various azimuths (fig. 2) . differeni parts ol the radiation pattern. 



Estimate of Combined Errors 

The combined effect ol all the errors mentioned 
above lias been estimated by comparing the two 
values of <>„ and I, obtained loi ea< h ol the 24 
earthquakes that were recorded at both the Beat 
Divide and Dillon Ranch sites. Each event has two 
spectra which were: (I) interpreted independently; 
(2) calculated from S-wave samples ol differeni 
lengths; (3) corrected l<»i attenuation ovei differeni 
propagation paths; and (4) affected differentl) by 
radiation pattern, scattering, and focusing. The esti- 
mated standard deviation ol ;i determination ol 



ANALYSIS OF RI si ITS 

Figure 4 is a ploi ol our interpretations of 210 
S-wave spectra ol 165 San Fernando aftershocks 'I Ins 

plot is similar to the Hanks and Thatchei (1 

Q„ — I diagrams. The top abs<issa is corner fre- 
quency, and the righthand ordinate is the 
low-frequency spectral amplitude (Q, corrected to 
.1 distance ol 10 km (12(10) = Q R 10 where R is 
hypocentral distance). The type of symbol used to 
represent each ol out spectra indicates the slop 
the- spec ti urn's high-liecprenc y asymptote ''see legend 



40 



30 



20 



CORNER FREQUENCY (cps) 
10 7 




40 



50 



70 



100 150 200 

SOURCE DIMENSION (meters) 



300 



400 



Figure 4. — Observed spectral parameters — corner frequency, $1(10) [= iloR/10, where Ho is low-frequency amplitude and R is hypocentral 
distance (km)], and slope of high-frequency asymptote (see legend) — and our interpretation (using the Brune (1970) model) in terms 
of source parameters — source dimension, seismic moment, and stress drop. Results of Trifunac's i!97-i study of accelerogram records 
of 13 large aftershocks are included. Error bars were obtained by comparing spectra of earthquakes simultaneousls recorded at the two 
different recording sites (fig. 2); the larger set applies to all the data, the smaller applies only to those having high-frequency slopes 
of — 3. Significance is attached to the sharp cutoff of stress drops at about 300 bars and, more speculatively, to the correlation between 
stress drop and spectral slope. 



Source Parameters for Aftershocks 81 



in fig. 4) . Only about 7 percent of the spectra have 
high-frequency slopes of — 1; the rest are about 
evenly divided between those with slopes of — 2 and 
those with slopes of — 3. 

To interpret these data in terms of source 
parameters, we have used the Brune (1970) model 
(with corrections from Brune 1971). Our measure- 
ments of fi 0) f c , and slope can be interpreted using 
any other model relating corner frequency to source 
dimension, for example, Kasahara (1957), Berck- 
hemer and Jacob (1968), Haskell (Savage 1972), 
and Aki (1972) . Results of Hanks and Wyss (1972) 
and Wyss and Hanks (1972) indicate that for 
moderate-size earthquakes, source parameters de- 
rived from the Brune (1970) model are in good 
agreement with field observations. There is no reason 
to believe the model does not apply to the smaller 
events studied here; however, our understanding of 
source mechanism is inadequate to decide with cer- 
tainty what model should be used for small earth- 
quakes. Our choice of the Brune (1970) model is 
one of convenience. In the Brune (1970) model, the 
source parameters, seismic moment (M ) , source 
dimension (r) , and stress drop (Act) are defined as 
follows: 



r = 



M 



Aa = 



2 .34/3 1_ 
2x f. 

47Tpit/3 3 fl 

tcRe<i> 

_7_ Mo 
16 r 3 



where /? is shear-wave velocity (3.5 km /sec) , R is 
hypocentral distance (table 1) , p is density (2.8 
gm/cm 3 ) , Re<p is the root mean square (rms) average 
of the radiation pattern (0.4) , and k is a correction 
factor for amplification upon free-surface reflection 
(taken to be 2, as for S//-waves) . The lower 
abscissa of figure 4 is source dimension, the left-hand 
ordinate is seismic moment, and the diagonal lines 
are lines of constant stress drop. Table 1 lists the r, 
M , and Act. 

In addition to our data, figure 4 includes points 
for 13 San Fernando aftershocks studied by Trifunac 
(1972). Trifunac used the Brune (1970) model to 
interpret Pacoima Dam (fig. 2) accelerogram records 
of the largest aftershocks (M L = 4.3 to 5.5) occurring 
during the 6 minutes following the main event. For 
the main event, Trifunac (1972) estimated a seismic 
moment of 1.5 X 10 26 dyne-cm and a stress drop of 



60 bars; Wyss and Hanks (1972) estimated 7 X 10 25 
dyne-cm and 14 bars, respectively. 

The error bars on figure 4 represent ± 1 standard 
deviation in our log M , log f c , and log Act determina- 
tions (it was necessary to estimate the errors in Act 
separately because the errors in M and r are not 
necessarily independent) . The unlabeled set of error 
bars was obtained using the procedure described 
under Estimate of Combined Errors. The smaller 
set, labeled — 3, was obtained using the same pro- 
cedure, with only those examples for which both 
events had spectra with slopes of — 3. 

We feel that, in large part, the range of values 
plotted on figure 4 represents a real variation in 
source dimension, moment, and stress drop. (See: 
Note Added in Proof.) The range is too large to be 
accounted for entirely by the known errors, and the 
symbols are not normally distributed about a point 
or line. There is no correlation between the source 
parameters and quality estimates given in table 1. 
Events with moments less than 10'* dyne-cm are 
missing from our data because their signal-to-noise 
levels were small. The upper limit of observed stress 
drops (300 bars) and the upper and lower limits of 
observed corner frequencies (30 Hz and 3 Hz, re- 
spectively) cannot be explained by any known experi- 
mental limitation. (Events with some of the largest 
stress drops had peak amplitudes 30 times less than 
the dynamic range of the instrument.) The com- 
bination of Trifunac's (1972) data (which include 
some of the largest aftershocks that occurred) and 
our data (which include events down to magnitude 
y 2 or less) is probably a representative sample of all 
San Fernando aftershocks having moments greater 
than 10 1 * dyne-cm. 

It is important to note that our sample of events 
has been influenced strongly by our choices of the re- 
cording system gain. The data set does not include 
all events that occurred within the range of the plot- 
ted points. When the amplifier gain was large, some 
large events were missed because of clipping; when 
the gain was small (or the amplifier bypassed) , nu- 
merous small events were missed because of low sig- 
nal level. If the system had been operated the entire 
8 days with the amplifier bypassed, our sample of 
events would have included only a few large, high- 
stress events. On the other hand, if the system had 
been operated at its highest gain during the entire 
period, the sample would have consisted of over a 



82 



San Fernando Earthquake of 1971 



thousand small events with generally small stress 

drops. 

There is a genera] correlation ol stress drop with 
moment; events with moments ol about 2/I0 1 
dyne-cm have stress drops, on the average, ol I to 10 
bars, whereas events with moments greatei than 10" 
dyne-cm have stress drops ol 100 bars on the average. 
Larger values of stress drop estimated for San Fo 
nando aftershocks are several orders ol magnitude 
larger than those previously estimated lor small 
earthquakes, although the smaller values are compa- 
rable to stress (hops obtained by Wyss (1970) Eoi af- 
tershocks of the 1968 Borrego Mountain earthquake 
and to those obtained by Douglas and R\all (1972) 
for Nevada microearthquakes. The large stress-drop 
events have corner frequencies that are from 5 to $0 
times greater than those predicted by the recently 
proposed scaling laws of Aki (1972) and the fault- 
length versus magnitude curve ol Wvss and Brune 
(19(>H). In fact, these large stress-drop aftershocks 
are more consistent with the early source-dimension 
versus magnitude curve of Press (1967). This lac t 
has important implications tor seismic discrimination 
between underground explosions and earthcpiak.es 
because these higher stress-drop events tend to have 
source parameters similar to those ol explosions. 

One of the most striking features of the data in 
figure 4 is the apparent upper limit of about 300 
bars for stress drop. Because the effect of errors 
would be to extend the data beyond any such limit 
in stress drop, the actual upper limit represented by 
these data is probably about 100 bars. This conclu- 
sion is based on the Aa error bars for spectra with 
slopes of —3 (because most of our data near this 
boundary have slopes of — 3). Thus, we interpret 
the data in figure 4 as representing a range of stress 
drops from less than 1 bar to an upper limit of 
about 100 bars. 

We speculate that this upper limit of 100 bars in 
stress drop is equal to the actual effective stress oper- 
ating; thus, events with stress drops of less than 100 
bars are fractional stress-drop events. This specula- 
tion is consistent with Trifunac's (1972) estimates of 
an effective stress of 85 bars and a stress drop of 
about 60 bars for the main shock. It is also consistent 
with an interpretation, using the Brune (1970) 
model, of the tendency on figure 4 for events with 
large stress drops to have steep slopes. In that model, 
spectra with slopes of —2 have stress drops equal to 
the effective stress while those with slopes of — 1 



smaller, fractional stress drop*. Although the 
Brune model docs (KM predict slopes of ~ ', for a/i- 
rniiilially averaged (rms) Spectra, it does not pre- 
clude slopes ol I at particular a/imutlis In fan it 
is reasonable- that the effect ol rupture might lead to 

observed correlation of steepei slopes with 
highei cornel frequencies. In the direction of rup- 
ture propagation, the cornei frequency is met' 
because high-frequency energ) is few used in this 

dnec tion. 1 lowevei . sue h fa using would be e-xp' 
to be ineffective at frequencies much higher than the 
coiner frequency because ol incoherence. 'I bus, 
steepei slopes would be correlated with higher cornet 
frequencies and higher stress drops. The relatively 
large numbei ol high-slope events would remain to 
be- explained, however. We- cannot determine for oes> 
tain whether the —3 slopes in our spectra are the re- 
sult ol propagation-path effects Ol of source effects — 
such as rupture propagation and those described by 
Savage (1972). The lack of correlation of high-fre- 
quency slope with distance is an argument against 
path effects as the explanation. The correlation be- 
tween steepei slopes and higher stress drops could be 
caused partly b\ a bias in the fitting process; if the 
spectia are forced to fit steeper slopes, the resulting 
corner frequencies and stress drops are increased. 
However, this effect was estimated above to be about 
25 percent in I and is therefore too small to ex- 
plain entirely the observed correlation. 

Finally, our data are further evidence of a large 
range in stress drops of small earthquakes. The fact 
that many of the San Fernando aftershocks had very 
high stress drops might suggest that parts of the 
source region were under a relatively high state of 
stress because of strain changes induced by the main 

Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks. 
The amplitude spectrum scale is relative, logarithmic units: time 
and log (frequency) scales are given at the bottom of each page. 
Spectra were obtained b\ Fourier-transforming the underlined 
part of each seismogram and correcting for instrument response 
and attenuation (assuming a Q of 250 and calculating h\pocentral 
distance from S — P times). Events recorded on two instruments, 
either at different sites (Bear Divide (B, and Dillon Ranch (D)) 
or on orthogonal components (EW and SS) at the same site, have 
two seismogram spectrum pairs, each with the same ID number 
but subscripted to indicate the site or component. A "c" below 
an ID number indicates that the corresponding seismogram was 
clipped. All but four spectra were fit to a curve having a constant 
low-frequency amplitude and a high-frequency asymptote with a 
slope from —1 to —3, resulting in the dashed curves through 
the spectra and the inferred values of low-frequency amplitude 
(Sl )> corner frequency tf c ), and high-frequency slope liable 1 and 
fig- 4). 



Source Parameters for Aftershocks 



r^JlMNV 



^Uflft|»M| 



f#^V 2 



^•-■ j *'C 



IP' 



h flif^^Ar-^v 




frflW 



44m 





*\ 1 SEC |*- 



'EW 



H 5 



NS 



z> 



Q. 
CO 



1 UNIT 



o 




4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5 .—Seismogram-spectrum pairs of San Fernando aftershocks. 



84 San Fernando Earthquake of i'J7l 



-^fM 



^ ■|J»1|y-»f*#y 



nHCj 




>EW 




'NS 





'EW 



/Aw 




'NS 



'EW 



*) 1SEC |* 




1 



2 4 6 8 10 20 40 60 

FREQUENCY (cps) 
Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 85 




*NS 



10 



EW 



-4fW\H\ 



10 



'\~v\/ 



NS 



%toWWW| 



iVvW^v* 



ii 



EW 



mw^^W 



|^':i%V^^'AVv 



"NS 



lull 




12 



-»| 1 SEC U- 






Q- 



Q 

ID 



o 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectruin pain, of San Fernando aftershocks — continued. 



66 San Fernando Earthquake of 1971 



^UVYf^W^l 




\/4/A 



>EW 



|1^4»W 



13 



N<, 



•~* — ^VV) 



il^fAv* 



14 



EW 




14 



NS 



| ^*M|t|i» is 



%/ 




rt 



16 



EW 



*\ 1 SEC |* 




4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 87 




16 



NS 



Vk^vwwA|| 



SJ 



to 



1/V 



17 



*H4# y| flM 



(ll^^w^ 



18 



f|||Wi^ 



19 



^Mfyv, 




20 




21 



-»|lSEC|« 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismograrn-spectrum pairs of San Fernando aftershocks — continued. 



88 San Fernando Earthquake of 197 1 





22 



EW 



s0}m/w 




22 



NS 



* * 




24| 



EW 



vyu 2 > s 



— >pmH^>v|| 




25 



EW 



25 



NS 



— »| 1 SEC |* — 






Q. 
C/5 



ID 



o 




There is no event 23. 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-Spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 89 



— Yt^^v^ ( ^vvv/ 




^V^wvr 




'•«Mww<wwW 








— *| 1 SEC (* 



26 



EW 



26 



NS 



27, 



EW 




27 



NS 



28 EW 
(c) 



28 



NS 



or 

t- 
o 

UJ 

to 



Q 



a. 



o 
o 




1 UNIT 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectruin pairs of San Fernando aftershocks — continued. 



90 San Fernando Earthquake of 1971 



■M»M 





/^ww^ 29 



M 




r. 








i\ifV\K^ 



-AiM'WMk, 



I A IPS-'fcV 



^^PfV^H^ 



30 



31 



32 



33 



-f|W»ft) 



w 



34 



-*| 1 SEC U — 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrutn pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 91 




35 



-JpfWi 




36 



-^W(|(^V^ 



37 



Vhi»im 



38 



|#~WWw 



Mif 




39 




40 



-H 1 SEC fe- 



et: 

I— 
o 






o 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



'J2 San Fernando Earthquake of 1971 




■-ty+WrWi\ 



--tyitytokto 




-irtfw* 




-HI 



f#\/V 



-») 1SEC 



41 



W^W^''-'^ 42 



43 



44 



45 



•-^^^ 46 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seisniogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 93 



*~-|Mwwto 




l/^vw 



47 



— ^iWVv^/,^ 




48 



jlwwv^ 



49 



~*w#WW 



mMfi™*Ar 



50 



— J^w^vv^l 




*4(WYrw 



51 




52 



-*| 1 SEC [< 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



!M San Fernando Earthquake of 19? ' I 



— ^W4Wfpj M^vAV^^ 




WiMf\^ 



- ^^wwiMvij 1. 4/y^Vv^^v-v 






53 



54 



55 



56 



ftp**** 



58 



— *| 1 SEC |<— 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



figure f.—Seismogram-spectrum pairs of San Fernando aftershocks— continued. 



Source Parameters for Aftershocks 95 




^f^fW 



^4*4^4 1 1 !| yYH /vV vv v ^ r 



wvw\/WIa 




Wv^vvvvVlA/ 





-») 1 SEC («- 



59 



7 p4^w||v)| l A w fl\aA^'Vv^^ 60 



61 



62 



63 



64 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seisniogram-spectrum pairs of San Fernando aftershocks — continued. 



96 San Fernando Earthquake of 1971 



■ViAA/' 




^l^i 




I^AwwYYf.^ 



65 



66 
(O 



67 
(0 



)v : 'i^Uv*^-^ 68 



69 



70 



-»| 1 SEC |* 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 97 




|^W<\ 



<iy-^t*^ 







— H 1 SEC|* — 



71 

(0 



72 



i«AAy v v v v w -iv^^-~' 73 



74 



75 



76 



o 

UJ 
Q- 






o 




1 UNIT 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



98 San Fernando Earthquake of 1971 




^m 



wJVm^w 




kf 





— f^W^-' 



^NHvi^VV*Y| 




yWWV 



— ») 1 SEC I*— 



77 
(O 



78 



79 



VVvwa 80 



81 



82 
(0 



o 



CO 






o 
o 




1 UNIT 



4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 99 



Mi 



m;'Wi^ 



— mW4 



J|j\%H^- 



-^M^M 



«fyv4y,l 



<#My| 




-|iv% 






— H 1 SEC }«— 



83 



84 



85 



86 



87 



88 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



100 San Fernando Earthquake of 1971 



;' .' :; V- 



i'H'l 



— ^AJVVl, 




^,?<HM 



HfyV^V-^' 



wmM^^^ 



-titlfk 



mi w 



A 



M 




1SEC 



89 



90 






~ 





91 



EW 



91 



NS 






'"^'TH 



ft 






92 



EW 



(C) 



92 
(c) 



NS 




4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 101 



'M^Vify 




111" " i |v 

1-1)1 1 



ww^i^y, 



H^lAW^I 



^yAw^/V 





— *\ 1 SEC f« — 



93 



EW 



93 



NS 



94 



EW 



I— 
o 



a. 
to 



o 



Q. 

< 



NS o 



95 



EW 



1 

UNI1 

T 



1UNIT 



95 



NS 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



102 San Fernando Earthquake, of 1971 



•wHwyW 



^,W'.mM 




4 6 8 10 20 40 60 

FREQUENCY (cps) 
Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 103 



-^MfV^A' 1 ^ 




-^My\W^ 



I irjfi I i 



-^#f 



I 



n/WWM 



^j 1 SEC |<— 



99 



EW 



99 



NS 



100 



-H^M^Vfll;^ 101 J_ 




103 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seisrnogram-spectrum pairs of San Fernando aftershocks — continued. 



KM San Fernando Earthquake of 197 1 



#», 



flftav^V^ 104 



€l 



\ 



§m^ ™ 



-*W4 



ite>H- 



'/Vi>/V* 106 



"'!!',■„, 



In I'i K ' 



^#(#« 



iftyto^'V 




o 

Q- 



O 



Q. 



O 
O 



KkaMJ 107 



i fm^ffit^W. 108 



1 

UNI 

T 



1 UNIT 



> 109 



— H i sec h — 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 105 



^fiMf' 



ww 



^ 



JfJlWA* 



*W Ipl f\J\f^M/^x 



HMH 



A4V\ 1 //wia^w-*vw 



-j^M^^ 



— *j 1 SEC 



110 



111 



112 



113 



114 



15 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



!()(> San Fernando Earthquake of 1971 



-tWfff 



116 



|WW 



Wkkf^i^^^ 



117 



«■ yU/'/VWV^j^ 



18B 



-t^u^rrM 



A-^y^^Mv-' 



WWAV » 8 ° 



Nv,WW 



119B 



4i 



119D 



-*| 1 SEC (*— 




4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 107 



-iwy#*VA 




120 




121 



—JrfSp*,\f«r>»s-/J* 



\ As/l 



HM4l^^i |^M WyMM^ 



-v^A; 



ifV IV 



iMIK 



HlH*^ 



tav\Vw^ 



122B 



122D 



123 



124B 



— »| 1 SEC |*— 




1 UNIT 



4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



I OK San Fernando Earthquake of 1971 



Ikkh 



'?>■■?'>■:.' 124D 



«)tM*»b 



^wh\^^^ 



^min 



fcl^^VM^ 



HjWW, 




— ^#4-' 



yttiVw 



— Hi sec 



V/m^vw- 125 B 



125D 



-N 



o 

Q. 
CO 




126 



o 
o 




127B 



-^. 



i 

1 UNIT 



T 



VV^aw^ 127 D 



\ 







\V*\ 



Y^Ap. 





/y 



■ 















<V 






',.-. 



flfc. 



1 2 4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 






Source Parameters for Aftershocks 109 



— ^^ 




/*\Ar\i*~ 128 B 



-M 



Mfihh* 



i^ty/Vi/l^W 




'fMM^flj 



i in 'i 



fuFi 



ff 



|hv^ 



foil 



'^lf,'4 



I^m* 



— »|lSEC|*- 



128D 



129B 



129D 



3 
a: 



a. 

C/"> 



o 



130B 



1 

1 UNIT 

T 



130D 




*r~^ 



1 j^Vfy 





V 




r A^^ j~ 



Y 




^iWb« 



> 



■; 



\ 



to 



i . Pi ' 



m 



fM% 



M 



Wl 



A' 1 Jl 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



1 10 San Fernando Earthquake, of 1971 




— <H* 1 ffwwrfsv-V-^WlA-oVj 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 1 1 1 



-ty^-toMM*f>' 



IflYy^ 



,v-~vvv-v 134B 



Wv ! /V'Atf-wV.^ 



WMfWWw^w- 



m 



!, |^VlilV»A^A^ 



-mM 



"1 



-MM^^Wp 



v^jirvi^ 



Attw**d 




— *) 1 SEC |* — 



134D 



135 



136B 



136D 



137B 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



1 12 San Fernando Earthquake of l'J7l 



»i/yVV»vrV^rM« 




137D 



If 



M^M/ww 



138B 



$$(pi0W 



138D 




V\fAryWW '39 B 



^^HMM^fw- 



139D 



ll^irtAAN-WAvvwvsv^ 




140B 
(c) 



lSECfe- 




4 6 8 10 20 40 60 

FREQUENCY (cps) 



Figure 5. — Seistnogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 113 



||M»4wyv^wf.Hv^ 




-1*4Mi^\vyw\M 



PVV^AW^ 143 B 



— »| 1 SEC |*— 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



I H San Fernando Earthquake of 197 1 



*ff< 



'W*»/VfW»%A. 



^/l V v4^/ v /^K^v-v"• 1430 



Y-^VMM, 




144B 



■mj^- 




144D 



"4k 





145 




146B 



-fji 



ff 



'v^l 146 D 



— *| 1 SEC I*— 




2 4 6 8 10 20 

FREQUENCY (cps) 



40 60 



figure 5. — Seismogram-spectrum pairs of San Fernando ajteishocks — continued. 



Source Parameters for Aftershocks 115 



-Htytl^ 



~^pf\ 




-^t^Mif^i 



H 1 SEC |« 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seistnogratn-spectrum pairs of San Fernando aftershocks — continued. 



1 1G San Fernando Earthquake of 1971 




^WMVV^! 



tWr 



— Af. '\An<vV* rw *vw\, /VW^ S 




*-r* — *w-^^>^-w*n/v^**VV| 




^vtfmwn 




151 



152 



153 



r ^^ v w,^A^,^ v j, l| ^U/^^vvavw^-^ 154 



155 
(c) 



'/• 156 



— *( 1 SEC(< — 




2 4 6 8 10 20 40 60 

FREQUENCY ( cps) 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 






Source Parameters for Aftershocks 117 



^iWwVWn 





-^fljU^fM 



|V»*W 




4</< 



HwK 



-»| 1 SEC I*- 



157 



EW 



157 



NS 



158 



EW 



158 



NS 



159 



EW 



159 



NS 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5 . — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



118 San Fernando Earthquake <>\ 1971 



^fMfit'f^ 1 



t 4 



160 



EW 



i\M 



WWiW 



160 



NS 



^Wf^ 






|jl t ^^ 161 



cc 

i— 
o 



CL 



J! '^'V*|J|^ 



162 < 

o 
o 



" — **(■{ 



j4^h^>M 



' 



A— 



•/ 



, 



XT- 




m \ffrVyHW\A^ 163 I ^ 

UNI1 

T 



1 UNIT 



Wj|f#if^ 



Mw 



164 




1SEC 










-i- 






T 1 





"N/ 



■ 






H\ 



T{- 



'' M 



f 









HJ 



^ 



M, 



i| , s 



4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



Source Parameters for Aftershocks 119 




'H/AWWWv 166 



^M¥(i l 0^ 




-nL 



ILf^ 1 



I Pi 
'...!■ i Lib 



i/jp/lirtA 



ViVv'V^AAAA. 168 



— H i sec K 




4 6 8 10 20 

FREQUENCY (cps) 



40 60 



Figure 5. — Seismogram-spectrum pairs of San Fernando aftershocks — continued. 



shock. Alternatively, these high stress-drop events 
could have had, for some presently unknown reason, 
higher fractional stress drops, with the effective stress 
for all events near 100 bars. It is interesting to note 
that the eight events recorded in December 1971, 10 
months after the main shock, all had stress drops of 
less than 10 bars. 

CONCLUSIONS 

More than 98 percent of the 220 S-wave spectra we 
calculated had a relatively constant amplitude at low 



frequencies, a well-defined corner frequency, and an 
estimated high-frequency asymptote with slope from 
— 1 to —3. About 7 percent of these spectra had 
high-frequency slopes of —1, with the rest about 
evenly divided between those with slopes of —2 and 
those with slopes of —3. Circumstantial evidence, 
based on comparisons of spectra of earthquakes si- 
multaneously recorded at two different sites and on 
lack of dependence of corner frequency and high-fre- 
quency slope on hypocentral distance, indicates that 
the spectral parameters fi„, f c , and slope represent 
seismic-source properties. Interpretation of these pa- 



120 



San Fernando Earthquake of 1971 



rameters using the Brune (1970) model gave seismu 
moments ol 10 M to 10'' dyne-cm, source dimensions 
of 50 to 500 m, ;iik1 stress drops ol I to 300 bars. 
The highei stiess (hops are several orders ol magni- 
tude greatei than obtained in previous studies ol 
small earthquakes and the cornei frequencies are 
about an order of magnitude greater than predicted 
by the scaling laws ol Aki (1072; and by the fault- 
length versus magnitude curve of W'yss and Brune 
(1968). There is a general correlation ol stiess drop 
with moment; events with largei moments have, on 
the average, larger stress drops. A relatively sharp 
cutoff of calculated stress diops around 300 bars and 
a correlation between high-frequency slope and stuss 
drop can be interpreted as indicating that the effec- 
tive stress lor the San Fernando aftershocks was 
about 100 bars and that tfie estimated range in ac- 
tual stress drops (100 to 1 bar) corresponds to a 
range in fractional stress drop (100 to 1 percent, re- 
spectively) . (See: Note Added in Proof.) Our data 
and interpretations are consistent with Trifunai 's 
(1972) results lor the main shock and 13 large after- 
shocks. 

Note Added in Proof: Recent experiments with 
spontaneous dislocations in foam rubber models sug- 
gest another explanation for the apparent low stress 
drops. Many of the slips in loam rubber models are 
multiple events along essentially the same slip sur- 
face, causing the overall time function to be con- 
siderably longer than for single events. This tends 
to shift the corner frequency to lower values than 
would be observed for a single event, thus giving 
erroneously large estimates of source dimension and 
erroneously low estimates of stress drop (propor- 
tional to the inverse cube of the estimated source 
dimension) . Further study is necessary to determine 
if such a mechanism is common in natural earth- 
quakes. 

ACKNOWLEDGMENTS 

The authors are particularly indebted to Don 
Miller who developed and maintained the recording 
system and to Dick Haubrich who gave critical ad- 
vice on spectrum analysis and statistics. Rob Wesson 
(USGS) and Tom Hanks and Jim Whitcomb (C.I.T.) 
provided the locations and origin times of after- 
shocks in figure 2; Gabette Hamlin assisted in data 
reduction and preparation of figures; Bob Winsett 
drafted the figures; Terry Barker wrote the computer- 
search program; and Irma Lieras and Elaine Black. - 



inoie typed tli' manuscript. Tom Hanki V. 
J hatcher, Petci tVfolnar, and Jim Sa\a^<- particip 
in helpful discussions; Petei rVfolnai alyj assisted in 
field operations. 

This research was supported by National S< j- 
Foundation Grant NS1 GA 10765, Seismu Data 
Analysis. 

KI I I Rl \f I s 

Aki, K<iiii, "Sf.ilin^ Law of Earthquake Source Time- 
Function," / he Geophysical Journal of the Royal 
nomical Sonny. Vol 31. Nov 1-3. Dec 1972, pp. J 

Berckhemer, If., and Jacob, K H "Investigation of the 
Dynamical Process in Earthquake Foci by Analyzing the 
Pulse Shape ol Bod) Wave*," Final icienlifu Report AF d\ 
(052) -801, Institute ol Meteorology and Geophysics, Uni- 
versity ol Frankfurt. Germany, Apr. 1966, 85 pp. 

Brune, fames V. "TectonM Stress and the Spectra of Seismic 
Shear Waves From Earthquakes," Journal of Geopl 
Research, Vol. 7".. No. 26, Sept. 10, 1970. pp 

Brune, James N "Correction," Journal of Geofjliyucal Re- 
search, Vol 76, No. 20. July 10. 1971. p. 5002. 

Douglas, Bruce M.. and Ryall, Alan, "Spectral Characteristics 
and Sttcss Drop for Microearthquak.es Near Fairview Peak, 
Nevada," Journal of Geophysical Research, Vol 77, No. 2, 
fan. Id. 1972, pp. 351-359. 

Hanks, Thomas C, and Than her, Wayne R., "A Graphical 
Representation of Seismic Source Parameters," Journal of 
Geophysical Research, Vol. 77, No. 23, Aug. 10, 1972, 
pp. 1393-1105. 

Hanks. Thomas C. and \V\ss. Max. "The Use of Body Wave 
Spectra in the Determination of Seismic-Source Parameters," 
Bulletin of the Seismological Society of America, Vol. 62, 
No. 2, Apr. 1972, pp. 561-589. 

Kasahara, K., "The Nature of Seismic Origins as Inferred 
From Seismological and Geodetic Observations." Bulletin 
of the Earthquake Research Institute, Vol. 35, Part 3, 
Tokyo. Japan, Sept. 1957. pp. 173-530. 

Press, Frank, "Dimensions of the Source Region for Small 
Shallow Earthquakes," Proceedings of the V ESI AC Con- 
ference on the Current Status and Future Progress for 
Understanding the Source Mechanisms of Shallow Seismic 
Events in the 3 to 5 Magnitude Range, La Jolla, California, 
22-24 March 1965, Willow Run Laboratories of the Institute 
of Science and Technology, University of Michigan, Ann 
Arbor. Feb. 1967, pp. 155-163. 

Savage, James C., "Relation of Corner Frequency to Fault 
Dimensions," Journal of Geophysical Research. Vol. 77, 
No. 20, July 10, 1972, pp. 3788-3795. 

Trifunac, Mihailo D., "Stress Estimates for the San Fernando, 
California, Earthquake of February 9, 1971: Main Event 
and Thirteen Aftershocks." Bulletin of the Seismological 
Society of America, Vol. 62, No. 3. June 1972, pp. 721-750. 

Wyss, Max, "Observation and Interpretation of Tectonic 
Strain Release Mechanisms," Ph. D. thesis, California Insti- 
tute of Technology, Pasadena, 1970, 239 pp. 



Source Parameters for Aftershocks 121 

Wyss, Max, and Brune, James N., "Seismic Moment, Stress, Wyss, Max, and Hanks, Thomas C, "The Source Parameters 

and Source Dimensions for Earthquakes in the California- of the San Fernando Earthquake Inferred From Teleseismic 

Nevada Region," Journal of Geophysical Research, Vol. 73, Body Waves," Bulletin of the Seismological Society of 

No. 14, July 15, 1968, pp. 4681-4694. America, Vol. 62, No. 2, Apr. 1972, pp. 591-602. 



Increased Seismic Shaking 
Above a Thrust Fault 



CONTENTS 


Page 




123 


Introduction 


123 


Seismic Shaking 


123 


Interpretation 


124 


Asymmetric Elastic-Strain Release 


124 


Multiple Reflection of Seismic 




Waves 


124 


Conclusions 


126 


References 



ROBERT NASON 

Earthquake Mechanism Laboratory 
Environmental Research Laboratories, NOAA 



INTRODUCTION 

The San Fernando earthquake involved some of 
the highest intensity of seismic shaking ever re- 
corded.. The high intensity of shaking also was shown 
in building failures (Stcinbrugge et al. 1971), shat- 
tered earth (Nason 1971) , and other unusual effects 
(Morrill 1971) . Most, if not all, of the high-intensity 
shaking occurred to the north of and above the 
north-dipping earthquake thrust fault (U.S. Geologi- 
cal Survey and the National Oceanic and Atmos- 
pheric Administration 1971). This paper presents 
two possible mechanisms that would produce in- 
creased seismic shaking above an earthquake thrust 
fault. 

SEISMIC SHAKING 

In the San Fernando earthquake, very strong 
seismic shaking occurred in the region north of the 
surface fault traces. This shaking produced: record 
accelerations, exceeding lg at the Pacoima strong- 
motion instrument (Maley and Cloud 1971); very 
heavy damage to some buildings and highway con- 
struction; and marked surficial geologic effects such 
as landslides, widespread soil cracking, and shattered 
earth (Nason 1971 and Barrows et al. 1971) as well 
as multiple-surface thrust faults. The shattered-earth 
effects are particularly impressive, for they indicate 
seismic shaking strong enough to destroy the internal 
structure of competent soil (figs. 1 and 2) . The shat- 
tered-earth effects suggest a possible seismic Modified 
Mercalli intensity XII in very localized areas. These 
effects occurred over a wide area north of the surface 
fault traces (fig. 3) , almost always on the tops of 
local ridges. 

INTERPRETATION 

The earthquake was generated by north-side up- 
ward movement on a north-dipping thrust fault 



123 



I '2.4 Sun Fernando Earthquake of J 97 J 




&#£%£■; 




Figure 1. — Shattered earth effect at Wallaby Street, Sylmar. 
Collapsed unfinished houses in background. 




Figure 2. — Shattered earth effect at Wallaby Street, Sylmar. 
Veterans Administration Hospital is behind hill at upper left. 



(U.S. Geological Survey and the National Oceanic 
and Atmospheric Administration 1971). The region 
of strongest seismic shaking was north of the surface 
fault traces and thus was above the north-dipping 
thrust fault. Did the special conditions of thrust-fault 
geometry and movement contribute to increased 
seismic shaking above the inclined fault? 

ASYMMETRIC ELASTIC-STRAIN RELEASE 

Studies of dislocation models of movement on in- 
clined thrust faults have shown that the fault move- 
ment is asymmetric, with greater displacement above 
the thrust fault than below the fault (Savage and 
Hastie 1966) , as shown in figure 4. The greater dis- 



placemeni above the thrust fault is because the- 
cal movement of the uppei block is not confiik 
the ground surface, while the lowei Mod is tightly 
confined by othei iock at its lower edgt J his conv 
pares with a partial confinement of movement on a 

strike-slip fault (confined by undisplaced rock at ei- 
ther end ol the active fault segment). Asymmetric 
displacement on the San Fernando thrust fault it 
shown well by leveling data (Tmrford et al. 1^71, 
Because ihe movement of the upper fault block is 
not confined, the uppei fault block will have much 
more complete elastic -strain relief than the lower 
fault block or a strike slip fault Mock. As the seismic 
wave energy is produced by the release of elastic- 
strain ener^v, the greatei clastic -strain relief above 
the thrust fault will mean production of more 
seismic energy per unit o| rock volume. Thiv in 
turn, will mean more energetic seismic waves above 
the thrust fault and, thus, increased seismic shaking 
above the thrust fault as observed at San Fernando. 
This mechanism would operate with any shallow 
earthquake thrust fault. 

MULTIPLE REFLECTION OF SEISMIC 
WAVES 



The ground surface and the inclined thrust fault 
plane form a wedge shape for the upper fault block, 
with the tip of the wedge at the surface fault trace. 
This wedge shape might partially "'trap' seismic 
wave energy and cause a concentration of seismic en- 
ergy near the tip of the wedge. The thrust fault 
would be a surface of at least partial reflection of the 
seismic waves and perhaps total reflection during the 
dynamic fault movement. The seismic waves in the 
block above the thrust fault would reflect back and 
forth between the fault surface and the ground sur- 
face, as shown in figure 5. This multiple reflection 
will cause an increased amount of shaking at the 
ground surface. The long duration of the strong 
shaking in the Pacoima record may represent accu- 
mulation of trapped seismic-wave energy caused by 
multiple reflection. 

CONCLUSIONS 



Both the effects of unconfined elastic-strain release 
above a thrust fault and of multiple reflection of 
seismic waves at the thrust fault may have contrib- 






Seismic Shaking Above a Thrust Fault 125 




■a 

B 



■a 

e 



120 San Fernando Earthquake <>j l'J7l 



uted to the lii^' 1 intensity ol seismi< shaking above 
the north-dipping thrust fault ai s.m Fernando. 
These effects also might l>c expected t" apply u > 
other earthquakes caused by thrusi fault movement 
anywhere in the world, I<m example, in Alaska 
(1964) or Assam in India (1897) . 



EPICENTER 



GROUND SURFACE 




Figure I. — Diagram .showing greater uplift and thus greater elastic- 
strain release in the block above a thrust fault (after Savage and 
Hastie 1966). 



N 




PACOIMA FAULT 


S 




EPIC 


ENTER 


DAM TRACE 
1 1 




\ v\ 


\ 111 


A A "7\ p 


^/\ s/ \ / ~^r / jS 




J \i\ -V 






■ f\ /\ X / ^^ S — 




\ \\ 




'\ l\ 1 A / r\ 


\rV//^/^ ^ 


^\ 


Vol 




WKi/a/ 






RN3S^ 












^^■IrFOCUS^^ 







Figure 5. — Seismic-wave paths from earthquake focus, with reflection 
at ground surface and tin list fault, showing difference of seismic- 
wave intensity on each side of fault. 



Rl I I KI N( I S 

Barrowi \ c. liable, J.E.. W«ba l l! (/ and Saul LL 
Map of Surface BreaJu ResultU I (he San I 

California Earthquake of February 9 1971, Prelin 
funt II. Plate I, California Division ol Mints and ' 
Sacramento, 1971, vale 1 '-') 000 

Burford, KO. (.asil<- ko Church | J' kmosluta w T., 

Kirln Sll Rullivcii R I ,,ri<l Savage, Jam's ( 

liminary Measurements ol TectooM Movement," The San 
Fernando, California, Earthquake of lrbruary 9, 1971 Gem 
logical Survey Professional Papet 733 U S Geological Suney 
and the National Oceanic and Atmospheric Administr 
Is Department ol tlie Interior and U.S. Department of 
Commero Washington, DC 197). pp. 80- »■ 

Maley. K.I'., and Cloud. W.K.. "Preliminary Strong-Motion 
Results from the San Fernando Earthquake of February 
9, 1971," The San Fernando, California, Flarthquake of 
February 9 . 1971, Geological Survey Professional Paper 733, 
IS Geological Sur\e\ and the National Oceanic and At- 
mospheric Administration. US. Department of the Interior 
and U.S. Department of Commerce, Washington, D.C., 1971, 
pp. 103-176. 

Morrill. B.J., "Evidence of Record Vertical Accelerations at 
Kagel Canyon During the Earthquake." The San Fernando, 
California, Earthquake of February 9. l u 'l, Geological Sur- 
rey Professional Paper 733. U.S. Geological Survey and the 
National Oceanic and Atmospheric Administration, U.S. 
Department of the Interior and U.S. Department of Com- 
merce. Washington, D.C.. 1971. pp. 177-181. 

Nason. Robert D., "Shattered Earth at Wallaby Street, Sylmar," 
The San Fernando, California, Earthquake of February 9, 
1971, Geological Survey Professional Paper 733, U.S. 
Geological Suney and the National Oceanic and Atmos- 
pheric Administration, U.S. Department of the Interior and 
U.S. Department of Commerce, Washington, D.C., 1971, 
pp. 97-98. 

Savage, James C, and Hastie. L.M., "Surface Deformation 
Associated With Dip-Slip Faulting," Journal of Geophysical 
Research, Vol. 71, No. 20, Oct. 15, 1966, pp. 4897-4904. 

Steinbrugge, Karl V., Schader. E.E., Bigglestone, H.C.. and 
Weers, C.A., Sari Fernando Earthquake, February 9, 1971, 
Pacific Fire Rating Bureau, San Francisco, Calif., 1971, 93 
pp. 

U.S. Geological Survey and the National Oceanic and At- 
mospheric Administration (Publishers) , The San Fernando, 
California, Earthquake of February 9, 1971, Geological Sur- 
vey Professional Paper 733, U.S. Department of the Interior 
and U.S. Department of Commerce, Washington, D.C., 1971, 
254 pp. 



Map of Surface Breaks Resulting 
From the San Fernando, California. 
Earthquake of February 9, 1971 



CONTENTS 



Page 

127 

128 

128 

128 

128 

129 
130 

131 
131 
131 

132 
132 
132 
133 
133 

133 
133 
134 



Introduction 

Major Zones of Surface Faulting 
Santa Susana Fault Zone 
San Fernando Fault Zone 
Mission Wells and Sylmar 

segments 
Tujunga segment 
Lakeview segment 
Additional Surface Faulting 
Surface Effects in Other Areas 
Juvenile Hall and Upper Van 

Norman Lake area 
Olive View Hospital area 
Southwestern Sylmar area 
Southwestern San Fernando area 
Granada Hills area 
Surface Effects of March 31 After- 
shock 
Shattered Ridce Tops 
Trenches Across Surface Breaks 
References 



Prepared in cooperation with the Los Angeles 
County Engineer and the Los Angeles County 
Flood Control District. Initially published in 
1971; reprinted by permission of California 
Division of Mines and Geology. Map of sur- 
face breaks is in pocket inside back cover. 



A. G. BARROWS 
J. E. KAHLE 
F. H. WEBER, JR. 
R. B. SAUL 

California Division of Mines and Geology 
Sacramento, Calif. 



INTRODUCTION 

On February 9, 1971, at 6:01 a.m., PST, an earth- 
quake of magnitude 6.6 [6.4] struck the Sylmar-San 
Fernando area of southern California. Geologists 
from the California Division of Mines and Geology 
commenced field investigations at once. Preliminary 
results, based on reconnaissance, were published by 
Kahle and others (1971) shortly after the earth- 
quake, as were results obtained by other organiza- 
tions (Kamb and others 1971; U.S. Geological Sur- 
vey Staff 1971). 

California Division of Mines and Geology staff 
began detailed field mapping of the geology, includ- 
ing surface effects, immediately after the initial 
reconnaissance. Information obtained through August 
1971 is given in this report. 

The following discussion includes sections on sur- 
face faulting, surface effects other than faulting, the 
Granada Hills aftershock of March 31, 1971, and 
findings from a series of backhoe trenches dug across 
surface features. No attempt has been made to in- 
clude landslide and cutbank failure information on 
this map except in the area of the Juvenile Hall. For 
discussions of landsliding see Morton (1971a; 1971b) 
and Youd (1971). Although most of the surface 
geologic effects of the earthquake are found within 
the area of this map, minor landsliding and forma- 
tion of settling cracks did occur elsewhere. Informa- 
tion about geological structures or stratigraphic units 
referred to in the following discussion can be found 
on the Los Angeles Sheet of the Geologic Map of 
California (Jennings and Strand 1969) or in reports 
by Oakeshott (1958) and Wentworth and others 
(1971). 



127 



128 



San Fernando Earthquake of 1971 



MAJOR ZONES OF SURFACE FAULTING 

At any given locality it may be difficult to 'lis 
tinguish surface breaks due to faulting from those 
due to other causes such as lurching, differentia] set- 
tling, landsliding, oi shaking. The criteria used to 
identify surface faulting are primarily continuity 
and linearity ol fracture, displacement oi lock units, 
and fresh movements along bedding planes in sedi 
mentary rocks. When the sin lace evidence is in un- 
consolidated material, the most common case, the 
most important c harae tei islic is c ontiniiity c ombined 
with any or all ol the othei c ritei ia. 

Surface faulting during the earthquake extended 
from the Bee Canyon area ol the- Santa Susana Moun- 
tains eastward across the Sylmar— San Fernando area 
of the northern San Fernando Valley to Big Tujunga 
Wash in Sunland. The major sin lace breaks are 
expressions of thrust faulting whereby land on the 
northern side was lifted above that on the south and 
shoved or thrust obliquely toward the southwest. The 
following is a discussion of the major /ones ol lault- 
ing proceeding from west to cast across t he area. I he- 
zones include the Santa Susana fault /one in the Bee 
Canyon-San Fernando Pass area and the San Fer- 
nando fault zone. 

Santa Susana Fault Zone 

Relatively small, left-lateral displacement occurred 
almost continuously along the principal fault of this 
zone for about 1.5 miles (2.4 km), from the San 
Fernando Pass area on the northeast to Bee Canyon 
on the southwest. The fault break is mostly in un- 
developed land and damage along it was restricted 
mainly to the Golden State Freeway (including Bal- 
boa Boulevard bridge) and several power lines and 
towers. 

About 300 feet (92 m) northeast of the freeway, 
the fault is well exposed (l), 1 with left oblique dis- 
placement of 3 to 4 inches (8 to 10 cm) ; here the 
fault dips about 20° northwest, with nearly vertical 
beds ol the lower Sunshine Ranch Member of the 
Saugus Formation overlying younger, gently south- 
east-dipping beds of the upper unnamed member of 
the Saugus Formation. To the southwest, along the 
freeway (2), abundant ground and concrete cracks 
suggest several smaller faults parallel to the Santa 
Susana fault, at least one with left-lateral offset. 



i Bold numbers identify locations of surface breaks shown as 
circled numbers on Map of Surface Breaks in pocket insert. 



I <> ihe southwest i>\ ihc- freewa) and beyond an 

ancient landslide- (3), the fault break is clearly de- 

(nie-d. Foi example, a line on the road to St. Vii 
t\< Paul Camp was displaced left laterally about 12 
inches (30 em; (4). From this area the tra< 
ground rupture extends west-northwest toward Be* 
Canyon where it seems to be absorbed along 
stiike ed bedding, and where abundant shat 
ridges and landslides mas have obscured fault move- 
ment (5). 

San leinando Fault Zone 

The San Fernando fault /one. as designated by the 
U.S. Geological Survey I S Geological Survey Staff 
1971; was divided In the Suivev into these segments 
which are, from west to east: Mission Wells, Sylmar, 
and I ujunga segments. That portion of the San Fer- 
nando fault /one between Little Tujunga and Big 
Tujunga Canyons, former!) eemsidered part of the 
Tujunga segment, is herein renamed the Lakeview 
segment because it coincides with the Lakeview thrust 
fault (Proctor 1970), making a total of four seg- 
ments c onsideied in this report. 

Mission Wells and S\lmur segments 

The Mission Wells segment strikes north-northeast 
from Osceola School, bends northeastward, and ex- 
tends to a point in alluvium about half a mile 
(0.8 km) from the southwest end of the Sylmar seg- 
ment. At least part of this gap between the two 
segments is marked bv a slight, south-facing break in 
slope, suggesting an older fault scarp (6). The al- 
luvium in the gap area is deeper (45 feet [14 m]) 
than to the west and east, as described by the Cali- 
fornia State Water Rights Board (1962) , which 
named this underground feature the Sylmar notch. 
Probably much of the earthquake energy from the 
fault below was dissipated into this relatively deep 
alluvium before it reached the surface. As a result of 
the earthquake, elevations increased to the north of 
the gap relative to the south just as they did relative 
to the active segments according to measurements of 
Burford and others (1971, p. 81) . 

Left-lateral offset, shortening, and downthrow on 
the south side occurred along the Mission Wells seg- 
ment but are less pronounced than along the Sylmar 
segment, as was the damage. The Mission Wells seg- 

o o o 

ment is best exposed along a cut in back of houses 
on the northwest side of Osceola Street (7), where 



Map of Surface Breaks 129 



it seems to dip 50° to 60° northwest. Just southeast 
of here, moderately south-dipping strata, probably of 
the Modelo Formation of late Miocene age, are ex- 
posed. Their presence here suggests left-lateral dis- 
placement of perhaps 1,200 feet (360 m) or more of 
the contact between Modelo Formation and younger 
Tertiary rocks to the west. Some activity is implied 
on this segment during the March 31 aftershock, as 
a tension crack just west of the fault on Osceola 
Street opened considerably wider at that time. 

The Sylmar segment of the San Fernando fault 
zone represents perhaps the most spectacular surface 
expression of tectonic activity in the entire earth- 
quake region. Cracks and welts in asphalt parking 
lots and streets, mole tracks in lawns, and other fea- 
tures of breaking and twisting of structure extend 
northeast in alluvial deposits from the southeast side 
of Hubbard Street opposite the former Carewell 
Convalescent Hospital (now called The Gables) , 
through the severely damaged commercial area (in- 
cluding Boys Market, now razed) along Glenoaks 
Boulevard (8). The segment continues northeast as 
a zone or swath as much as 1,200 feet (360 m) wide, 
with severe damage to many houses in Sylmar and 
San Fernando. It bends gently almost due east, and 
continues to Foothill Boulevard where a modern 
apartment building (now razed) was severely dam- 
aged, and extends spectacularly across the Foothill 
Freeway (9). From here the segment narrows, and 
extends along the base of a low hilly area, across the 
concrete channel in Pacoima Wash, and bends south- 
east along the base of a ridge of the foothills east of 
Sylmar where it apparently dies out. Projected south, 
the segment would extend toward the Tujunga seg- 
ment and probably comes to the surface in the San 
Fernando Industrial Park (10). 

Where exposed by trenches, the dip of the fault 
generally is obscure because of the relatively poorly 
consolidated nature of the material cut by the fault 
at the surface, even where trenches cut prominent 
south-facing scarps; but, in one backhoe trench just 
northeast of the Foothill Freeway (T13) , a crushed 
zone implies a dip of 52° north on the fault. To the 
east of this locality, the segment strikes essentially 
parallel to the bedding of the Towsley (?) Formation 
exposed locally just north of the segment; and the 
dip of the fault segment may be similar to the dip of 
these rocks. On Gladstone Street (11), about 100 
feet (30 m) northwest of the segment, strata dip 
about 55° to 60° north; and, very near the east end 



of the segment, strata dip about 35° north. Indicative 
of previous very late Pleistocene or Holocene fault 
movement in the immediate area, but inactive in the 
present earthquake, is a nearly vertical fault exposed 
on Gladstone Street 200 feet (61 m) north of the 
principal break. Here, older alluvium is faulted down 
at least 2 feet (60 cm) to the south against Towsley (?) 
Formation. Similar faults are exposed to the west 
along the cuts of the Foothill Freeway — one of which, 
having a total reverse offset of 50 feet (15 m) or 
more, was active during the earthquake. 

About a quarter mile (0.4 km) (12) north of the 
Sylmar segment, in the vicinity of Harding School 
and Alta Mesa Convalescent Hospital (formerly 
Highland Sanitarium) , is an area of faults and 
ground cracks in older alluvium. The breaks trend 
essentially east, parallel to the strike of the bedding 
of the Saugus Formation that is exposed nearby 
beneath thin, older alluvium. The faults are com- 
monly slightly right lateral and down slightly on the 
north; they extend east toward Lopez Dam but are 
obscure there. The dip of the faults was not deter- 
mined, but may be along bedding planes of the 
Saugus Formation, which dips about 70° north. Dam- 
age to structures in the area was minor to moderate. 

Tujunga segment 

The surface features that comprise the Tujunga 
fault segment extend from the vicinity of the San 
Fernando Industrial Park (13) eastward along Foot- 
hill Boulevard where, just east of Vaughn Street, the 
northeast sidewalk and curb were lifted abruptly 
several feet relative to the pavement (14). The 
breaks continue across the mouths of Lopez, Kagel, 
and Little Tujunga Canyons and disappear near the 
mouth of Cassara Canyon. In some places (15) (16) 
the breaks of the Tujunga segment define a single, 
continuous fault-line scarp, whereas in other places 
the segment consists of numerous, interrupted, locally 
multiple (17), scarps and cracks that very closely 
approximate the change in slope at the base of the 
foothills. Asymmetrical compression ridges and mole 
tracks are the southernmost surface features of the 
thrust faulting. Abundant tensional cracks and high- 
angle fault scarps are common immediately north of 
the thrust-fault scarps. 

An average of five measurements of the approxi- 
mate amount of shortening across the thrust fault in 
the orange groves of Middle Ranch (16) is 3.6 feet 
(1.1 m) . The lateral component of slip for faults 



130 



San Fernando Earthquake of 1971 



of the Tujunga segment is predominantly left lateral 
(18) (19) (20). 

The scarps ol the Tujunga segment attain theii 
greatest height, exceeding ;i yard (I m) , neai the 

western end (14). In general, the scarp is between 
16 inches (-10 cm) and 20 in* Iks (50 cm) high ovei 
the most continuous stretches .\\\d it diminishes to- 
ward the east. 

The low-angle dip, ranging from 10 north to 40 
north, can be observed where the trace ol the thrust 
fault crosses stream canyons (21) (22) (23). Accu 
rate, near-surface measurement ol the attitude ol the 
lank plane was made in several trenches (T3) (T4) 
(T8) . A few feet beneath the surface the fault plane 
parallels the bedding in the Modelo shale, sandstone, 
and siltstone but flattens out to horizontal (T8) or 
even slightly south-dipping (14) where details were 
revealed in trenches. Slickensides hearing N. 50° E. 
plunge 22° N. on clayey layers (T8) that coincide 
with the fault plane. 

Lakeview segment 

Surface breaks along the Lakeview segment can be 
traced eastward from the ridge west of Kagel Canyon 
to the northernmost scarp across Little Tujunga 
Canyon and with some discontinuity through the 
foothills, across Cassara, Oliver, and Schwartz Can- 
yons about 1,400 feet (0.4 km) north of their mouths 
to Big Tujunga Wash. Scarps can be followed for an 
additional 1.5 miles (2.4 km) in the alluvium of 
the wash. 

From Kagel Canyon the surface trace can be fol- 
lowed eastward as far as the east side of Little Tu- 
junga Canyon where it dies out at the base of the 
hills. Where exposed by a small slide just to the west 
of Little Tujunga Road (23), the trace shows shale 
of the Modelo Formation lying on top of uncon- 
solidated bouldery cobble gravel. These units are in 
fault contact and, although the fault did move in 
this earthcpiake, it did not move an amount sufficient 
to account for the total thrust component of at least 
12 feet (3.8 m) which can be measured here. 

The fault trace can again be found on the first 
ridge east of Little Tujunga from where it can then 
be traced with some confidence to Big Tujunga 
Wash. In this stretch of the fault, the surface traces 
are much more continuous than the gaps. 

Movement has taken place on a fault plane that 
dips northward from nearly horizontal in some places 
(25) to 60° in others (26). The sinuous fault trace 



ciossc-s ridge tops, hillsides, and canyon bottoms. 

Landslide complication! along the- trace at fust led 
us and othei workers in the ana M'S Geolo 
Survey Stafl 1971, p. 71; to discount the- possibility 
ol fault movement here. However, de-tailed mapping 
ol the surface effects has indicated that significant 
movement did indeed <>< < ui on tin I 
me-nt with as much displacement as measured on the 
othei segments ol the- San Fernando fault /one-. 

Some- imbricate oi sympathetic movement can be 
detected below the- mam trace between the breccia 
unit and the boulder gravel (27) and in a few places 
there seems to have been differential movement of 
the texks on adjacent blocks above the thrust (28). 

An accumulated horizontal thrust component ol at 
1,450 feet (442 m) can be measured on the 
fault near Oliver Canyon I he- age of the alluvial 
gravel undei the- thrust is not known. However, this 
much displacement could have taken place in 25.000 
to 70.000 years from a series oi similar earthquakes 
(4- to 6-ft displacement) occurring at intervals of 
100 to 200 years. 

In the coarse alluvium of Big Tujunga Wash the 
scarps locally resemble erosional cut banks but the 
continuity of the trace which traverses sand depejsits, 
gravel deposits, bulldozer cuts (29), bridle trails, and 
vegetation covered areas (30) of the flood plain 
makes it easy tej follow. Cracks occurred in soft sand 
and soil along the trace and debris fell down the face 
of the scarp. Considerable ponding of the alluvium 
has occurred where the fault crosses the stream (31). 

At the base of the cliff near the mouth of Ebey 
Canyon (26) a scarp with a vertical displacement of 
about 3 feet (1 m) and vertical slickensides formed 
between bedrock and the alluvium. Caving obliter- 
ated much of this evidence within three months after 
the earthquake. The scarp can be traced farther east- 
ward through the alluvium to where there was a 
left-lateral displacement of about 3 feet (1 m) on 
Oro Vista Avenue. The vertical component of move- 
ment is much less here than farther west and appears 
to decrease eastward. A bedding-plane fault is visible 
on the north side of the hill on which Bill Lane 
Camp is situated (32). 

Several kinds of evidence have been found which, 
when considered together, substantiate movement on 
the Lakeview segment. Firstly, the well-defined sur- 
face trace is nearly continuous, and surface displace- 
ment is consistent on ridge tops and in canyon 
bottoms — always up on the north. However, old 



Map of Surface Breaks 131 



landslides and thick accumulations of slope wash 
have masked the surface trace along some hillsides. 
Secondly, distinctive landslides, restricted to the 
trace, occurred at the time of the earthquake (33) 
(34). Shale of the Modelo Formation was thrust out- 
ward on the slope enough to drop as rockfalls. Debris 
and dust partially cover the slope below the trace, 
simulating "skin-type" slides or soil failures. Com- 
monly, the slope below the break is undisturbed 
although, in some places, the material both above 
and below the thrust plane has been exposed. 
Thirdly, the rock unit under the thrust is in some 
places a breccia and elsewhere is a mixture of breccia 
and alluvium. The breccia consists exclusively of 
angular chips and debris derived from the Modelo 
Formation. In the mixed unit the breccia is similar 
and the alluvium consists of layers of interbedded 
well-rounded pebbles and sand grains. Weathering 
has changed the appearance of the breccia unit and 
the shales above the fault plane since the earthquake. 
The color contrast has been enhanced — the shale 
turning dark brown and the breccia nearly white or 
light gray. Under the breccia unit there is an older 
alluvial unit consisting of unconsolidated, horizon- 
tally bedded, boulder conglomerate, greater than 30 
feet (10 m) thick, with well-rounded clasts derived 
from the basement complex of the San Gabriel 
Mountains. 

ADDITIONAL SURFACE FAULTING 

Faults other than thrusts also were active during 
the earthquake at places away from the major zones 
of thrusting. A type of fault in which the dip and 
strike of the fault parallel the dip and strike of en- 
closing strata is known as a bedding-plane fault. It is 
exemplified by the Veterans fault (35) (Kamb and 
others 1971, p. 51) and by the Oak Hill fault (Tl) 

(Kamb and others 1971, p. 48) in Lopez Canyon 
where a very prominent, partly overhanging, 32-inch 

(80 cm) scarp was formed. In these examples the 
north side moved up in north-dipping strata. Else- 
where (36) (37) the north side moved down in 
north-dipping strata by amounts equal to or greater 
than south-side-down faults. 

Several faults that transect bedding also moved 
during the earthquake (38) (39) (40). The Kagel 
fault (Hill 1930) was active over a stretch 1.75 miles 

(2.8 km) long. The surface breaks along the trend 
of the Kagel fault are not continuous and exhibit 



the greatest vertical offset (41) (42) along ridge 
crests whereas there was commonly no surface rup- 
ture in the canyon bottoms except in Bartholomaus 
Canyon (43). On Kagel Mountain (44), west of 
Cassara Canyon (40), and along Yerba Buena Ridge 
(45) faults developed that appear to displace bed- 
rock and cross ridge tops with the displacement up 
on the downslope side. The scarps (40) west of 
Cassara Canyon may be related to an adjacent ancient 
landslide. 

West-southwest of the Mission Wells segment lies 
a zone of faulting which damaged the Golden State 
and San Diego Freeways. On the west end of the 
zone, the fault activity may have extended into frac- 
tured, clayey beds which dip south and strike west- 
southwest into the lake area (46). Faults mapped in 
this area previously by Oakeshott (1958) and others 
have been projected toward Lower Van Norman 
Dam. 

To the northwest (47) are two fault breaks, nu- 
merous ground cracks, cracks in the Golden State 
Freeway, and shaking effects. The faults and ground 
cracks mainly strike west-northwest, parallel to the 
strike of bedding in the Saugus Formation, whose 
dip ranges from 25° to 60° northeast. 

SURFACE EFFECTS IN OTHER AREAS 

Juvenile Hall and Upper Van Norman Lake area 

Considerable ground cracking and damage oc- 
curred in the area from Van Gogh School eastward 
beyond the San Fernando Valley Juvenile Hall, a 
distance of nearly 2 miles (3 km) . The cracks occur 
mostly in deposits which range from sand to fine 
sand and gravel, and to a lesser extent in fill. The 
area overlies the Olive View fault as projected south- 
west through the area from exposures northeast of 
Olive View by Merifield (1958, plate 1) ; it also 
overlies the projected northeast trace of the Mission 
Hills syncline shown by Oakeshott (1958, plate 1) 
and by Merifield (1958, plate 1) . None of the cracks 
can be attributed directly to faulting although at 
depth beneath alluvium faulting may have been a 
factor; no major activity occurred on northeast- 
trending faults where they are exposed northeast of 
Olive View (48). The cracking was attributed by 
Youd (1971, pp. 105-109) to sliding along water- 
saturated layers near the ground surface within the 
general area where the water table is high. Such 



132 San Fernando Earthquake of 1971 



layers subsequently were exposed in bat khoe treru lies 
dug at the Juvenile Hall (M), which was severely 
damaged by sliding as well as by shaking. I he Juve- 
nile Hall slide extends southwest toward LJppei Van 

Norman Lake and also includes the Southern Pacific 
railroad tracks, which were dramatically hem, a por- 
tion of the Golden State Freeway, and also the 
strongly shaken Pacific Inieitie Terminal (50). 
Severe sliding also occurred all around the edges of 
the northern part of Uppei Van Norman Lake (51). 
Landslide-type cracks also occur in the heavily dam- 
aged Van Gogh School aiea and loi about hall a mile 
to the north-northeast (52); also to the cast in the 
fill for the Jensen Filtration Plant (53); and directly 
north of the Juvenile Hall area and probably to the 
north-northeast for about half a mile (54), although 
these latter cracks might he attributed to faulting, 
as they arc aligned in a north-northeast to northeast 
direction. Such landslide-type cracks also occur at 
locality (55), where two houses were severely dam- 
aged. Cracks possibly attributable to landsliding are 
in the area around locality (56). One section of the 
Golden State Freeway and a northeastern part of 
Lower Van Norman Lake also may have slid (57). 

Just southeast of Upper Van Norman Dam, a 
trench for a water line exposed two fairly strong re- 
verse faults offsetting the contact between Saugus 
Formation and Pacoima Formation (older allu- 
vium ?) of late Pleistocene age; apparently they were 
not active during the February 9 earthquake (58). 

Olive View Hospital area 

Severe tensional and compressional cracking of 
asphalt roads and parking lots occurred on the 
grounds of the Olive View Hospital; very few co- 
incided with significant ground cracks. The most 
severe ground cracks occurred around the founda- 
tions of the new main hospital building or were 
associated with the Los Angeles Department of Water 
and Power Maclay Aqueduct which traverses the 
ground from west to east. All cracks appear to be the 
result of severe shaking in soft alluvium which is 
known from borings to be greater than 40 feet 
(12 m) deep. Cracking could not be ascribed directly 
to faulting although the possibility that faulting oc- 
curred at depth cannot be discounted and it may 
have contributed to the severity of the shaking in 
this area. One very low-angle slide was seen in allu- 
vium or fill in the center of the grounds and some 



slides on steepej slopes Occurred on the low hill in 
the northeast comei of the Olnc- \ u mds. 

Slides occ lined m fill used foi the Foothill 
south ol tlu- grounds. A west northwest trending 
/one ol relative!) strong street and ground nao 
tends I mile (1.6 km, or more yjiitheast of the 
hospital area. The cracks are mostly displa' • 
on the vjuth and may have resulted from movement 
along a fault here (59). 

Southwestern Syhnm area 

Additional ground and asphalt cracks occur in the 
area of the heavily damaged Svlmar Industrial Park 
and the LI Dorado Avenue School (60). Most of the 
ciacks arc in asphalt streets, parking lots, and the 
school plavground, but some extend into tfre allu- 
vium, especially just northeast of San Fernando Road 
(60). Northeast of Herrick Avenue lies a well-defined 
but relatively weak fault break which trends north- 
west (T14) . 

One relatively prominent crack, formed at the time 
of the earthquake, cuts across Roxford Street (61). 
There are other parallel, west-northwest trending 
cracks, mostlv from just south of bradlev Avenue to 
about midwav to Herrick Avenue: these all seem to 
predate the earthquake, though some were active 
during the event. 

Southwestern San Fernando area 

Some street and ground cracks, trending mostly 
east, are in the western part of San Fernando. Dam- 
age here occurred especially to older houses and to 
some churches (62). The area, underlain by older (?) 
alluvium, is approximately at the projected, con- 
cealed junction of the Mission Wells fault from the 
north, the Mission Hills fault from the west, and the 
Verdugo fault from the southeast (as shown on the 
Los Angeles Sheet of the Geologic Map of Cali- 
fornia) . To the southeast, the hills at Jessup Park 
were examined but no fault activity could be seen 
(63). To the west (64) only surficial pavement 
cracking occurred above the projected trace of the 
Mission Hills fault, though considerable damage oc- 
curred at Alemany High School, Holy Cross Hospital, 
and at the new Indian Hills Medical Center build- 
ing. The high school was also damaged during the 
March 31 aftershock. New cracks also opened then 
at the corners of the sidewalks at the base of the 
Rinaldi Street overpass of the San Diego Freeway at 



Map of Surface Breaks 133 



Rinaldi Street. In the downtown shopping area of 
San Fernando (65), intense damage is attributed to 
shaking of older buildings on alluvium, as only sur- 
ficial cracking in pavement occurred. 

Granada Hills area 

In the area of Granada Hills west of Lower Van 
Norman Lake and, generally along Balboa Boulevard, 
many houses were damaged (66). Here ground crack- 
ing cannot be related to faulting. The cracks are 
mainly along or near contacts of fills with bed- 
rock (67). 

SURFACE EFFECTS OF MARCH 31 
AFTERSHOCK 

The impact of the damaging March 31 after- 
shock was most severe in the vicinity of Rinaldi 
Street and Wilbur Avenue in Granada Hills (75), 
although the epicenter of this event was reported to 
be about 2.5 miles (5 km) to the south-southeast. 
The magnitude was 4.6 as reported by the California 
Institute of Technology. Ground cracks opened in 
older alluvium south of Rinaldi in the vicinity of 
Yolanda Avenue where two houses were severely 
damaged; cracks opened between bedrock and fill 
north of Rinaldi along Yolanda. In addition, some 
cracks that opened during the February 9 earth- 
quake were reactivated during this one. Surface 
effects of the aftershock may lie along the general 
trend of the Devonshire fault zone as mapped to the 
northwest in bedrock and projected southeast be- 
neath alluvium by Saul (1971). 

SHATTERED RIDGE TOPS 

Some ridge crests in the foothills have a striking 
"exploded" appearance resembling plowed fields 
where the soil looks as if it had been heaved upward 
by a sharp blow from below. Such shattering is most 
common along those crests underlain by sandstone 
and conglomerate strata that have a soil cover com- 
monly less than 2 feet (60 cm) thick (68) (69) (70). 
Between Lopez and Little Tujunga Canyons shatter- 
ing is either localized along certain strata (71) (72) 
or concentrated where there is especially angular 
topography locally (73) (74). An excellent example 
of the latter is around Camp Karl Holton in Marek 
Canyon. Elsewhere, shattering is localized along the 
uppermost sandstone layers of the Towsley (?) For- 
mation. In the overlying coarser, clastic, sedimentary 



layers of the Saugus Formation, it is almost absent at 
the contact immediately east and west of Kagel 
Canyon (72). 

TRENCHES ACROSS SURFACE BREAKS 

Brief descriptions of the findings in 15 backhoe 
trenches logged by the California Division of Mines 
and Geology in cooperation with F. Beach Leighton 
& Associates are listed below. Logs of the trenches 
were made by E. G. Heath and R. H. Dickey of F. 
Beach Leighton & Associates, who independently 
dug Trench 1, and by J. E. Kahle and A. G. Barrows 
of the Division of Mines and Geology. Logs of the 
trenches may be consulted in the Los Angeles office 
of the Division of Mines and Geology. 

Trench 1 : Lopez Canyon. Trench across the Oak 
Hill fault scarp. Bedding plane fault strikes 
N. 75°W. and dips 62°N. and is nearly coinci- 
dent with attitude of sandstone, siltstone, and 
conglomerate strata. Displaced base of slope wash 
and alluvium is 32 inches (81 cm) down on the 
south side. 

Trench 2: Lopez Canyon. Trench across mole track 
of Oak Hill fault in unconsolidated fill and 
alluvium. Although surface is cracked no fault- 
ing was observed in the trench. 

Trench 3: Ridge north of Carl Street. Trench 
across compression ridge exposed well-defined 
single fault plane that strikes east-west and dips 
44°N. and coincides with attitude of bedding. 
Fault juxtaposes shale of the Modelo Formation 
on the north over conglomerate with coarse 
sandy matrix which may be an alluvial fan 
deposit. 

Trench 4: Ridge west of Blue Star Trailer Court 
and north of Paxton Street. Trench across 2-foot- 
high (60 cm) scarp in soil exposed near-surface 
aspect of fault plane that separates debris of the 
Modelo Formation containing shale chips, peb- 
bles, and cobbles on the north from old alluvium 
which is poorly bedded. Fault plane dips north 
15° near northern end of trench, bends over 
near the surface, and dips shallowly southward. 

Trench 5: Pacoima Wash near Newton Street. 
Trench across 1-foot (30 cm) scarp of Sylmar 
fault segment. Fault could not be seen in the un- 
consolidated, bouldery alluvium. Caving limited 
exposure to 4-foot (1.2 m) depth. 



\M Sun Fernando Earthquake of 1971 



Trench 6: Big Tujunga Wash, south oi creek. 
Trench across 20- to 'l / \-\\u\\ (50 60 cm; scarp 
in modern, flat-lying, bouldery alluvium l)i 
rectly beneath the surface offset, a jumbled zone 
dips approximately 45' northward but coarse- 
ness ol materia] and lack ol markei units made 
it difficult to determine whether oi not faulting 
occurred. 

Trench 7: Big Tujunga Wash, north ol creek. 
Trench across 15-inch (38 cm) scarp. Flat-lying 
to shallowly south-dipping, sandy and bouldi 
moist alluvial layers which are overlain by soil 
and fill vaguely appear to be folded beneath 
scarp. May represent a dispersion oi a discrete 
fault plane in unconsolidated materials. 

Trench 8: Blue Star Trailer Court, west side of 
Lopez Canyon. Trench across 2.3-foot (70 cm) 
scarp in graded bedrock surface. Movement dur- 
ing earthquake took place on two parallel fault 
planes that coincide with the N.80°W. strike 
and 32° N. dip of bedding in Modelo siltstone 
and sandstone. Near the surface, however, the 
northernmost fault plane bends over and be- 
comes horizontal. Trench also exposed shallowly 
dipping, undisturbed fault contact between over- 
lying, highly contorted Modelo sandstone strata 
and reddish-brown mudflow-like alluvial mate- 
rial. 

Trench 9: San Fernando Valley Juvenile Hall 
grounds. Trench across main trace of northern 
set of cracks in football field. Main crack could 
be traced in moist sandy and silty soil contain- 
ing abundant roots to a depth of 5.5 feet (1.7 m) 
to the upper surface of a gravelly layer where it 
appeared to stop. This may suggest that move- 
ment took place along the surface of the gravelly 
layer. 

Trench 10: San Fernando Valley Juvenile Hall be- 
tween inner and outer compound. Trench across 
trace of southern set of cracks. Main crack strikes 
N. 10°W. and extends nearly vertically 9 feet 
(2.75 m) to bottom of trench through layers of 
silty sand, many with high organic content. 

Trench 11: South of San Fernando Road opposite 
San Fernando Valley Juvenile Hall. Trench in 
open field across sand boil. Light brown, sand- 
filled crack could be traced 9 feet (2.75 m) from 
center of sand boil to bottom of trench in dark 
brown silty sand. The filled crack represents the 
fracture through which material traveled to sur- 



face during formation of the sand boil lis total 

depth is Hid noun. 

<h 12: Vacant lot at 12670 Gladstone Avenue, 
Sylmai Trench a<ioss surlacc- ciacks ali 
with fault s<aips east and west of lot. No tim 
nificant breaks could be- sc -en in the- iinconsoli! 
eland pebbly to bouldery conglomerate and 
inter layered sand strata although strata app 
to bend to conform to surface- warp or yaip. 

Trench 13: North shouldei of Foothill Freeway, 
west cjf Mac las Avenue. 1 rc-nch across 1-foot (30 
cm, east west scaip 01 warp. Fault plane dipping 
52 N. could be traced as a zone of looser mate- 
rial separating gravelly and cobbly deposits with 
a reddish, sandy matrix on the north from adobe- 
like materia] of possible mudflow origin on the 
south. 

Trench 11: West side- ol Tylei Street. 200 feet 
"id in northeast ol Herrick Avenue, Sylmar. 
I rench auoss northwest-striking crack. Not pos- 
sible to tiac e c iac k in loose trash and fill e\; 
in walls ol ticne h. 

Trench 15: West o| road to St. Vincent de Paul 
Camp, east ol Ike Canyon. Trench across minor 
ciacks possibly coinciding with the trace of the 
Santa Susana fault. Not possible to follow cracks 
in loose, powdery soil exposed in walls of trench. 

REFERENCES 

Burford, R.O.. Castle, R.O., Church, J.P., Kinoshita, W.TJ 
kirbv, S.H.. Ruthven, R.T., and Savage, J.C.. "Preliminary 
Measurements of Tectonic Movement," The San Fernando, 
California, Earthquake of February 9, 1971, Geological Sur- 
vey Professional Paper 733. U.S. Geological Survey and the 
National Oceanic and Atmospheric Adminisuation, U.S. 
Department of the Interior and U.S. Department of Com- 
merce. Washington, D.C., 1971, pp. 80-85. 

California State Water Rights Board, "City of Los Angeles 
vs. City of San Fernando, et al.," San Fernando Valley 
Reference Report of Referee No. 650079, Superior Court, 
Los Angeles County. Calif.. Vol. I. 258 pp.. 36 pis.: Vol. II, 
various pages, July 1962. 

Hill. M.L.. "Structure of the San Gabriel Mountains North of 
Los Angeles, California," California University Publications 
in Geological Sciences, Vol. 19, No. 6, University of Cali- 
fornia Press, 1930, pp. 137-170. 

Jennings. C.W., and Strand, R.G., Geologic Map of California, 
Olaf P. Jenkins Edition, Los Angeles Sheet, California 
Division of Mines and Geology, Sacramento, 1969, scale 
1:250.000. 

Kahle, J.E.. Barrows. AG.. Weber, F.H.. Jr., and Saul, R.B., 
"Geologic Surface Effects of the San Fernando Earthquake," 



Map of Surface Breaks 135 



California Geology, Vol. 24, No. 4-5, 1971, pp. 75-79. 

Kamb, Barclay, Silver, L.T., Abrams, M.J., Carter, B.A., 
Jordan, T.H., and Minster, J.B., "Pattern of Faulting and 
Nature of Fault Movement in the San Fernando Earth- 
quake," The San Fernando, California, Earthquake of 
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D.C., 1971, pp. 41-54. 

Merifield, P.M., "Geology of a Portion of the Southwestern 
San Gabriel Mountains, San Fernando and Oat Mountain 
Quadrangles, Los Angeles County, California," M.A. thesis, 
University of California, Los Angeles, 1958, 61 pp. 

Morton, D.M., "Seismically Triggered Landslides Above San 
Fernando Valley," California Geology, Vol. 24, No. 4-5, 
1971a, pp. 80-82. 

Morton, Douglas M., "Seismically Triggered Landslides in the 
Area Above the San Fernando Valley," The San Fernando, 
California, Earthquake of February 9, 1971 , Geological Sur- 
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National Oceanic and Atmospheric Administration, U.S. 
Department of the Interior and U.S. Department of Com- 
merce, Washington, D.C., 1971 b, pp. 99-104. 

Oakeshott, Gordon B., "Geology and Mineral Deposits of 
San Fernando Quadrangle, Los Angeles County, California," 
California Division of Mines Bulletin 172, Feb. 1958, 147 
pp. 



Proctor, R.J. (Compiler) , "Geologic Map and Sections Along 
the 4.4-Mile Sunland Tunnel," B-20262, Metropolitan 
Water District of Southern California, Los Angeles, July 
1970 (unpublished map, scale 1:12,000). 

Saul, R.B., "Effects of the San Fernando Earthquake in the 
Oat Mountain Quadrangle," California Geology, Vol. 24, 
No. 4-5, 1971, p. 83. 

U.S. Geological Survey Staff, "Surface Faulting," The San 
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Department of Commerce, Washington, D.C., 1971, pp. 
55-76. 

Wentworth, Carl M., Yerkes, R.F., and Allen, Clarence R., 
"Geologic Setting and Activity of Faults in the San Fer- 
nando Area, California," The San Fernando, California, 
Earthquake of February 9, 1971, Geological Survey Pro- 
fessional Paper 733, U.S. Geological Survey and the Nar 
tional Oceanic and Atmospheric Administration, U.S. De- 
partment of Commerce, Washington, D.C., 1971, pp. 6-16. 

Youd, T. Leslie, "Landsliding in the Vicinity of the Van 
Norman Lakes," The San Fernando, California, Earth- 
quake of February 9, 1971, Geological Survey Professional 
Paper 733, U.S. Geological Survey and the National Oceanic 
and Atmospheric Administration, U.S. Department of the 
Interior and U.S. Department of Commerce, Washington, 
D.C., 1971, pp. 105-109. 



Effects of 

San Fernando Earthquake 

as Related to Geology 



CONTENTS 


Page 




137 


Summary 


138 


Geologic Setting 


141 


Comparison with Borreco Mountain 




Earthquake 


141 


Transitory Effects 


142 


Permanent Effects 


142 


Tectonic Ruptures 


142 


San Fernando Fault and Related 




Ruptures 


143 


Lakeview Thrust 


144 


Lower Santa Susana and Related 




Faults 


146 


Veterans Fault 


146 


Honby Ruptures 


147 


Camp Holton Rupture 


147 


Zones of Bending 


147 


Uplift, Tilting, and Horizontal 




Displacement 


147 


Landslides 


147 


San Fernando Reservoir Landslides 


147 


Juvenile Hall Landslide 


148 


Olive View Landslides 


148 


Camp Holton Slope Failures 


148 


Kagel Mountain Landslide 


148 


Other Ground Failures 


149 


Shattered Ground 


149 


Structural Damage 


151 


Estimates of Average Loss 


151 


Distribution of Damage 


152 


Effects of Deformation 


152 


Correlation and Implications 


152 


Predicting the Faulting 


153 


Conclusions 


153 


References 



Publication authorized by Director, 
U.S. Geological Survey. 



R. F. YERKES 

U.S. Geological Survey 
Menlo Park, Calif. 



SUMMARY 

The epicenter of the moderate (magnitude 6.4) 
San Fernando earthquake was located only 4 miles 
northeast of the urbanized San Fernando Valley; the 
earthquake was the first in historic time to be accom- 
panied by tectonic ruptures of the ground surface in 
the metropolitan Los Angeles area. The ruptures 
were caused by left-oblique reverse movement on the 
San Fernando fault, which dips about 35°NE. be- 
neath the northern part of the valley (and the south- 
westernmost San Gabriel Mountains) , thus account- 
ing for the relatively intense shaking effects north of 
the fault. Although the attitude and movement of 
the San Fernando fault are dissimilar to those of 
San Andreas-type faults, the faulting was in response 
to the same stress system and was the most recent ex- 
pression of a long-established pattern. 

Permanent surface deformation accompanying the 
faulting included: the east-trending zone of tectonic 
ruptures that traversed the urbanized valley floor 
and that coincided with evidence of prior faulting; 
uplift, tilting, and southwestward shifting of an area 
of more than 75 square miles of the southwestern- 
most San Gabriel Mountains; and numerous slope 
failures. Transitory effects included the most severe 
ground motions ever recorded; the strong motions 
were recorded more extensively than for any pre- 
vious earthquake. 

Unusually severe shaking, locally exceeding 50 
percent of g, characterized the mountain-front belt 
about midway between the epicenter of the main 
shock and the surface ruptures. Shaking strong 
enough to severely test pre-1933 structures, accompa- 
nied by measured horizontal accelerations of 10 to 
20 percent of g, extended southward into the down- 
town areas of Los Angeles and Pasadena 25 miles 
from the epicenter. More than 25 percent of all 



137 



138 



San Fernando Earthquake <>\ 1971 



dwellings in the area of heavy shaking north ol the GEOLOGIC SETTING 



rupture /one had losses exceeding 5 percent of 
preearthquake markei value. Damage was concen 
trated along the rupture /one and along boundaries 
between relatively unconsolidated alluvial deposits 
and harder, denser rocks; such boundaries in this 
area commonly coincide with east and southeast 
trending, north-dipping reverse faults ol the Santa 

Susana and Siena Madrc systems that hound the San 
Gabriel Mountains on the south. 

The San Fernando fault is not known to have 
ruptured previously dming historic time, and al- 
though segments of it had been mapped, no evalua- 
tion of their potential activity had been attempted. 
Abundant evidence ol geologically recent faulting 
along the same trend indicates the activity of the 
zone. The San Fernando earthquake is one ol the 



I he- San Fernando earthquake occurred in the 

souiliucsic inmost San Gabriel Mountains, in the 
central part of the Transverse Ranges geomorphic 
province ol southern California (fig. I). 'I he promi- 
nent east-trendin and valleys of the province 

contrast sharply with the northwester 1\ trends of the 
Coast Ranges to the northwest and the Peninsular 
Ranges Los Angeles Basin on the south. The pres- 
ent-day geometry ol the cmstal bloc ks in this n 
is such that the San Gabriel Mountains block south- 
west ol the- San Andreas fault is constrained and 
compressed against the- erustal blcxk north of the 
it bend" ol the San Andreas where it forms the 
north boundary of tire San Gabriel Mountains. Such 
compressive deformation over the last 5 to 10 mil- 



smaller events produced by the same stress system lion years has thrust the mountain block relatively 

that produced the 1857 Fort Tejon (magnitude 8 + ) southward up and over adjoining lowlands such as 

and 1952 Kern County (magnitude 7.7) earth- the I.os Angeles Basin and San Fernando Valley 

quakes. along s\siems of reverse or thrust faults such as the 




Figure 1. — Index map of major faults in southern California, showing relation of San Fernando Valley, February 9 (1971 ) earthquake 
epicenter and rupture zone to Transverse Ranges, San Andreas fault, and larger earthquakes (shown by stars and dates), and historic 
ruptures (jagged lines), attributable to same stress system as the San Fernando earthquake. Arrows show inferred principal component 
of relative movement. Adapted from Hill (1954, fig. 1). 



Effects of Earthquake as Related to Geology 139 



Santa Susana and Sierra Madre. The most impressive 
product of this deformation is the bold southern 
front of the San Gabriel Mountains, which rises 
5,000 to 9,000 feet above the lowland surface to the 
south. Thus, the February 9, 1971, earthquake and 
reverse faulting were expressions of a long-estab- 
lished pattern. 

The San Fernando earthquake is attributed to dis- 
placement on a buried north-dipping fault beneath 
the southwesternmost San Gabriel Mountains, north 
of the San Fernando Valley. The map pattern of epi- 
centers (see epicentral area, fig. 4) is bisected by the 
surface trace of the San Gabriel fault, an important 
member of the San Andreas fault system. The map 
trend of the San Fernando fault is similar to that of 
the San Gabriel and San Andreas faults in this area, 
N.65°-70°W., but instead of being nearly vertical, 
tiie fault is inclined about 35°NE. toward the San 
Andreas, and thus passes beneath the trace of the 
San Gabriel fault. The dip of the San Fernando 
fault is such that it intersected the surface as a zone 
of tectonic ruptures along the north margin of San 
Fernando Valley where it coincides with evidence of 
earlier faulting. 

The sense of displacement was also dissimilar to 
that characteristic of the San Andreas; instead of 
right-lateral (horizontal shear) movement on a 
near-vertical fault, the displacement was reverse in 
nature — the mountainous block north of and above 
the fault moved relatively southwestward, up and 
over the San Fernando Valley south of the fault. As 
measured by total displacement across the 1971 rup- 
tures, the mountain block was uplifted as much as 7 
feet and shifted westward as much as 6 feet relative 
to the valley block on the south. Horizontal (com- 
pressive) shortening normal to the trend of the rup- 
tures was as much as 3.5 feet. Resurvey of a preearth- 
quake net of gravity stations in the area shows that 
the significant gravitational changes attributable to 
the faulting occurred in the mountain block north 
of the rupture zone and that the changes (decreases 
in attraction of 0.1 to 0.36 mgal) are consistent with 
the measured uplift of the mountain block (Oliver 
1973) . 

Although many segments of the mountain-front 
fault system had been mapped and interpreted in the 
context of this geologic history, the abundant but 
relatively unobtrusive evidence of late geologic activ- 
ity along the trace of the February 9 ruptures had 
not been widely recognized or appreciated. However, 



similar evidence relating to the Sierra Madre system 
east of Pasadena had been recognized and published 
(Wentworthetal. 1970) . 

The San Fernando Valley area (fig. 2) is located 
in a depositional basin that dates from middle Mio- 
cene time (about 15 million years ago) ; the basin is 
floored and bounded on the north, east, and south 
by crystalline basement rocks (Wentworth and 
Yerkes 1971). The basin is inferred to be 15,000 to 
20,000 feet deep in its central part; the upper 50 to 
1,000 feet of basin fill are relatively unconsolidated 
alluvial sands and gravels (Q 1} Q L . of structure sec- 
tion, fig. 3) . 

The valley is bounded on the north and northeast 
by prominent east-to-southeast-trending reverse and 
thrust faults of the Sierra Madre-Santa Susana sys- 
tem. At and near the surface, these faults form prom- 
inent topographic and geologic boundaries such as 
steep, eroded scarps in sedimentary rocks, north-dip- 
ping contacts along which crystalline basement rocks 
have been thrust over young sediments, and impedi- 
ments to the flow of ground water in alluvium (fig. 
3) . Several faults, such as the Verdugo, also coincide 
with pronounced residual Bouguer gravity gradients 
(Corbato 1963, fig. 7) , indicating that the surface 
density contrasts extend to considerable depth. Sub- 
sidiary faults, such as the east-trending Northridge 
Hills and Mission Hills faults (figs. 2 and 3), are 
recognized on the basis of surface evidence and 
ground water impediments in young materials, both 
of which indicate recent geologic activity. 

The Sylmar area, where damage was most intense, 
is underlain by a thin veneer of unconsolidated al- 
luvial deposits, which in turn overlies steeply north- 
dipping sand and gravel beds of the Saugus Forma- 
tion (included in Q J; figs. 2 and 3) . The Saugus in 
this area forms an east-trending syncline; its north 
limb is overturned and overthrust by older rocks of 
the mountain block along the Olive View fault and 
other faults of the Santa Susana system (see north 
end of section, fig. 3) . The south limb of the syn- 
cline is interpreted as being cut by another north-dip- 
ping reverse fault, a segment of the San Fernando 
fault, which ruptured during the February 9 earth- 
quake. 

In the San Fernando city area, the February 9 
zone of tectonic ruptures closely followed the surface 
trace of a ground water impediment that had been 
mapped previously (figs. 3 and 6) . Along the eastern 
part of this segment, the ruptures also followed an 



HO 



San Fernando Earthquake of 1971 



eroded fauli scarp ai the south i-d<^- ol an uplifted furnish strong evidence of geologically recent activity 
area of old stream terrace deposits (Q , easi ol the along this segment >>\ th< San Fernando fault. 
north part ol section line N S, fig. 2) . '1 l><- displaced In the fall ol 1970 ground wain was at depths ex- 
water table and surface scarps in alluvial deposits ceeding 50 feet below the surface throughout most ol 




m 






n v 



DOTJUtt - 

Alluvium 




x : : : : : : : :W-'' 

*0& 



Q„, Terrace deposits and upper 
Miocene to Pleistocene 
sedinentary rocks 

T, Upper Cretaceous and Tertiary 
sedimentary rocks, minor 
middle Miocene volcanic rocks 

Basement complex 



Normal, reverse, or strike-slip fault 



. . FAU.I.T ' 
• '■'■'<■'' 



_* A * »_ 

Thrust or detachment fault 



'.•'r^LP 



F E R N AN D 



:-:hs<& '■■ :•:•.■ 




LE Y 



. 








**&£&& 



;: : : : : : :s: : A : N:i : A: : : : : : x^QM^ < :'■:'■ • ^©"^: : -:- : 




MILES 



Figure 2. — Generalized geologic map of I.os Angeles-San Fernando Valley area showing epicenter (box) and rupture zone along San 
Fernando fault, February 9, 1971. Geologic section (fig. 3) along line A'-S. Adapted from Jennings and Strand (1969). 



Effects of Earthquake as Related to Geology 141 



San Fernando Valley (fig. 3) , except in the vicinity 
of the San Fernando Reservoirs. With that excep- 
tion, saturation of near-surface materials by ground 
water apparently did not contribute significantly to 
the earthquake damage. 

COMPARISON WITH BORREGO MOUNTAIN 
EARTHQUAKE 

The San Fernando earthquake was comparable in 
magnitude (6.4) to the Borrego Mountain earth- 
quake of 1968 (6.5) , which was the last large earth- 
quake to affect southern California. That latter 
earthquake occurred 145 miles southeast of Los An- 
geles on the margin of the Imperial Valley on the 
Coyote Creek fault, a vertical (?) fault of the San 
Jacinto fault zone (a part of the San Andreas sys- 



tem) ; this earthquake had only minimal effects in 
the Los Angeles metropolitan area. Although compa- 
rable in magnitude, the effects of the two earth- 
quakes were quite dissimilar, especially in maximum 
fault displacement, size of affected area, and maxi- 
mum intensity (table 1) . 

TRANSITORY EFFECTS 

In addition to forming the first historic tectonic 
ruptures within the Transverse Ranges, the San Fer- 
nando earthquake made engineering history by 
being not only unusually well and widely recorded, 
but also by being unexpectedly intense and thus 
much more destructive than might have been antici- 
pated. The more prominent transitory effects in- 
cluded: about 7 seconds of very strong shaking 



Inferred extension 
Northridge Hills 
Fault 



Mission Hills segment, 
Son Fernando fault 
{Ruptured 2/9/71) 



Olive View 
fault 

San Gabriel 

Mountains 

Q 2 





VERTICAL=4X HORIZONTAL 



Figure 3. — North-south geologic section across San Fernando Valley, showing thickness of valley fill ((),, Oj) and relation to late Tertiary 
sedimentary (T) and basement rocks (g), faults, ground-water impediments, and top of ground water as of fall 1970. Based on 
California State Water Rights Board (1962, pis. 5B and 6) and unpublished data supplied by the Los Angeles Department of Water 
and Power. 



M2 San Fernando Earthquake <>f 1971 

Table l .—Comparison of the Borrego Mountain and Son Fernando 
earthouahet 

Boi rego Ml ' s.m Fernando 
Apr. 8, 1968 I eb 9, 1971 

Richtei magnitude 6.5 6.4 

Estimated fo< al depth 12 mi 5 mi 

Maximum measured horizontal M'< g a( 40 I | - .ii 4 mi 

acceleration and epicentral mi 

distance 

Length of surface rupture 20 mi 9 i mi 

Dip of fault vertical(?) aboul '.VNl.. 

Type of movement right-lateral left-obli 

i ... i . 

Maximum displacement (net slip; 1 ,25 ft 7 '> ft '-' 

Maximum intensity (Modified VII VIM XI 

Merealli) 

Area of intensity VII or greater 550 sq mi <\ mi 

1 Data from summary, Youd and Castle ' 1970). 

2 Components of net slip: 4.92 feet of reverse dip slip, 6.25 feet 
of left-lateral, and 2.0 feet of transverse (shortening normal to 
trend). 

(Modified Merealli intensities VIII-XI and meas- 
ured horizontal accelerations greatei than 25 pen cut 
of g) over an area of about 140 square miles (en- 
tered on Sylmar (fig. 4); and about 10 seconds ol 
moderately strong shaking (intensity VII and meas- 
ured horizontal accelerations between 8 and 25 per- 
cent of g) over an additional area of about 885 
square miles that includes all of San Fernando Val- 
ley, the northern part of the Los Angeles Basin, and 
nearby parts of the Santa Clara River Valley. 



PERMANENT EFFECTS 

The most significant permanent effect ol the San 
Fernando earthquake, one not previously recorded 
in the metropolitan Los Angeles area, is the zone of 
tectonic: ruptures that extends across the north margin 
of the main San Fernando Valley from its west edge 
at Mission Wells eastward to the mouth of Big Tn- 
junga Canyon (fig. 5) . Other important permanent 
effects include movement on a segment of the lower 
branch of the Santa Susana thrust fault west of Syl- 
mar; formation of surface warps or narrow zones of 
lateral bending without ruptures; regional uplift and 
tilting of the land surface north of the rupture zone; 
destructive landslides in the Olive View area and in 
the vicinity of the San Fernando Reservoirs; local 
differential settling, lurching, and failure of alluvium 
and artificial fill; and numerous small areas of in- 
tensely shattered soil on ridge tops around the north 
margin of the valley. 

Tectonic Ruptures 

The following review of the tectonic ruptures is 
based on field studies by the U.S. Geological Survey 



Stafl (1971) , Barrowi el al. (1971) , and Kami, et al. 
(1971). 

San Fernando Fault <n\<l Related Rupturei Al- 
though a rathei broad zone of tectonic rupturei 
formed in the Sylmai s.m Fernando area (location 
A, fig V fig. '/ . the laigest displacementf were con- 
centrated along the rupturei in the southern part of 

this /one I Ins pail ol the /one coincide! VCTy 'losely 

with the previouil) mapped trace of a ground water 
impediment (fig. 0,, interpreted to have been 
formed by repeated faulting along the same trend 
(Wentworth et al. 1971, p. 1 

The broad area ol short rupturei just west of IV 
coima Wash and north of the main rupture zone do- 
tation B, fig. 5) is underlain by an upfaulted c-ro- 
sion.il remnant of lemiconsolidated stream terrace 
gravels (Q s in fig. 2). 'I he eroded fault scarp at the 
rupture /one along the south margin of this remnant 
is about '!'> feel high. The ruptures in this area 
north of the main /one are chiefly tensional, down- 
thrown on the north, and most show small compo- 
nents of i ight-lateral separation (fig. 6) . 

The most prominent and continuous ruptures east 
of San Fernando formed along the base of the hills 
between San Fernando and the mouth of Big Tu- 
junga Canyon 7 miles to the east. However, the con- 
tours of uplift (fig. 7) show that the east-trending 
axis ol the /one of uplift continues directly eastward 
into the foothills along the trend of the Mission 
Wells-San Fernando segment of the rupture zone. 
The prominent ruptures in Lopez Canyon, about 0.5 
mile north of the canyon mouth (location C, fig. 5), 
may thus represent the main or dominant fault trace. 
This trace is difficult to locate in the hills because it 
is obscured by numerous slope failures and patches 
of shattered earth: the only recognizable scarp along 
its trend was formed in the bottom of Lopez Can- 
yon. This zone of ruptures also consistently dips 
much more steeply northward than does that at the 
south margin of the hills (65 c -72 : versus 15 "— 37 c ) ; 
the dips are subparallel to bedding in adjoining bed- 
rock in each case. The hill-front zone of ruptures 
(location D, fig. 5) may thus be a secondary effect, 
the response of the frontal segment of hills to thrust- 
ing of the main mass to the north. 

Evidence of at least two earlier events of similar 
faulting along the hill-front zone of ruptures is ex- 
posed in a cut bench just west of the mouth of 
Lopez Canyon. Each of these faults thrust surficial 
deposits or bedrock over younger material. Neither 



Effects of Earthquake as Related to Geology 143 

of them was disturbed by the faulting of February 9, Lakeview Thrust.— A preexisting fault, the Lake- 
which instead formed a new rupture just upslope view thrust of Proctor (1970) , was reactivated along 
from the older ones. the hill front near the mouths of Oliver and 



118°30' 




EXPLANATION 
N vtT^'' '': ' ^'V', ' V. ' - / 0- , unconsolidated sand and gravel 



Q , seraiconsolidated sand and gravel 

Wh| T, sandstone, pebbly sandstone, or 
siltstone 



Metamorphic or plutonic rocks 

Epicentral area; contains more than 
95% of 700+ well-located aftershocks; 
box indicates main-shock epicenter 

Location and value (7„ G) of maximum 
X 29 measured horizontal ground 
acceleration 

f^..,\ Approximate boundary and inferred 
intensity of shaking 



•x. •••••■• .• 

\ 
\ 



*28 - \ 



SAN 



F E R N A N J) 

VALLEY 

,,. . X23 






VII 



\ X24 



X18 



X28 



X22 



• -V ■ • \ ■ - - i 
< .^>v. {.->.*> a: .-.v. 

. '. fej -•—■X 'ir-r^- --■»-. 



SANTA 

MONICA 



*12 
X20 



18 



X13 




20 



8X 



X6 



LOS 

ANGELES 
"~ TA S I N 



MILES 



Figure ■/. — Map of transitory effects of February 9 (1971) earthquake. Epicentral area contains more than 95 percent of more than 700 
well-located aftershocks recorded between time of main shock and April 23, 1971 (data from Allen et al. 1971, Wesson et al. 1971, 
and written communications). Measured maximum horizontal accelerations from Hudson (1971. table 1 ); those shown in parentheses 
are estimates based on interpolation of a seismoscope record (Seed et al. 1971) and analysis of failure of Olive View Hospital (Structural 
Engineers Association of Southern California 1971). Inferred intensity of shaking and approximate boundaries from N.H. Scott (1971). 



I'M San Fernando Earthquake of 1971 



Schwartz Canyons, about 2 miles cast ol Little Tu- 
junga Canyon (location E, fig. 5). In this area, Mio 
cene silt stone previously had been thrust ovei young 
terrace deposits (1 ovei Qj, fig. 2) thai underlie the 
ridges between these canyons. Although details are 
obscured by landsliding, the 1971 faulting involved 
thrusting with vertical displacements as great as 5.3 

feet on a fault that (lips northward between 1 ~> and 
45°. 

Lower Santa Susana and Related faults. — A mile- 
long segment of the lowei Santa Susana tlnusi west 
of Sylmar ruptured discontinously during the earth- 
quake, offsetting a road about 1 loot in a left-lateral 
sense (location F, fig. 5). Evidence foi a tectonu oii- 



gin of tins rupture includea its coincidence with a 

previously mapped thrust fault that locally < ut 

stream terrace deposits, local continuity across i 
and valleys, and movement not clearly attributable 
to slope failure. Soil on many of the ridge tops above 
the fault was shattered severely. Opposed to a sirictly 

tectonu origin, on the Othei hand, is the fact that 
ihe lowei Sanla Susana llnust is penetrated by sev- 
eral wells in t he Cascade oilfield immediately to the 
west, none- ol which was disturbed by movements 
sulhc ieni to c ause damage. 

\ shorter, subparallel rupture formed near the 
north end, but about 0.3 mile east of that described 
above (location (., fig. 5). Movement on this rup- 



II9°|S0' 






118° 22' SO' 



34° 
22' 30" 



Tectonic rupture, showing dip, boll on 
*s downthrown side, number shows 
vertical seporot ion (inches) 

Direction and amount (Inches) 
of horizontal separation 



t^... 



vajrt % . . 









iff 

A 



j 



Zone of loteral distortion; arrows 
show direction of bending 



Amount of horizontal shortening (inches) 
across rup'ure zone 

Fissure or scarp bounding londslide, 
hochures on downslope side 

X 

Shattered eorth on ridge top 



3 4<^ 

22' 30' 










26C 20 



w? c l 



H 



23 






3_4« 

15 



neoUo' 



II8 |22'30" 



Figure 5.— Map of permanent effects of the February 9 (1971) earthquake, showing zones of surface ruptures, lateral distortion, and slope 
failures. Underlined tetters refer to text. Data from Youd (1971) and field iiwestigations by Sharp and Yerkes. 



Effects of Earthquake as Related to Geology 145 



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146 San Fernando Earthquake of 1971 



Mi»i»0' 



11° 

it' so" 



M O 






^ 



vo i\ > . 



34° 

IS' 



■:** 




V.' 






\ 



7 






| 

1 



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(HelUj 



S 10 FEE 

1 I I I I I | 

VECTOR SCALE 



J — ! 1 ! i . l 




X' 

18* 






ll«° 22' SO" 



Figure 7. — Map of northern San Fernando Valley area, showing elevation changes since I960 or 1963 in meters (and ft) relative to bench 
mark labeled "Held" (data from liurford 1971 ) and observed horizontal displacements showing vectors in feet (data from Savage 1971/. 



ture could be attributed to local slope failure, but 
the rupture also traversed ridges and valleys and is 
parallel to faults of the Santa Susana system. 

Veterans Fault. — An east-trending rupture about 0.3 
mile long, the Veterans fault of Kamb et al. 
(1971), formed at the north-dipping, previously 
faulted contact between the stream terrace deposits 
and the Saugus Formation just west of the mouth of 
Pacoima Canyon (location H, fig. 5) . Movement was 
reverse and vertical displacement of the north block 
was about 7 inches. Although the rupture intersected 
several houses and streets, most of the considerable 
damage in this particular area is attributable to the 
intense shaking along this mountain-front zone; this 



rupture thus may be a secondary effect along a 
preexisting fault. 

Honby Ruptures. — A unique instance of ground rup- 
ture occurred in alluvium north of the Santa Clara 
River at Honby (location M, fig. 5. north border) . 
This narrow zone of discontinuous en echelon rup- 
tures is about 1 mile long and trends about X.25 E.. 
subparallel to and nearly coincident with the north- 
west margin of the aftershock pattern. Vertical dis- 
placement across ruptures was as much as 4 inches up 
on the west, and right-lateral displacement was as 
much as 2.5 inches. Considerable minor damage, such 
as rupturing of pavement, curbs, and sidewalks, ac- 
companied the displacement. Along the same trend 



Effects of Earthquake as Related to Geology 147 



on both sides of State Highway 14, south of Santa 
Clara River, considerable localized structural damage 
accompanied failure of artificial fill and cracking of 
natural ground. 

Camp Holton Rupture. — A preexisting north-dip- 
ping fault in bedrock just north of Camp Karl 
Holton Juvenile Facilities, 1.5 miles northeast of the 
mouth of Little Tujunga Canyon (location N, fig. 5) , 
showed evidence of movement involving about 6 
inches of left-lateral displacement, which accounts 
for severe damage to the gymnasium building. Al- 
though the fault cuts across the south end of a steep 
ridge of bedrock, it is not certain that the movement 
should be considered tectonic. 

Zones of Bending 

A unique feature of the surface deformation asso- 
ciated with the earthquake was the formation of sev- 
eral narrow zones of horizontal bending, either as Z- 
shaped connections between offset rupture zones, as 
at the west end of the hill-front zone east of San Fer- 
nando (location I, fig. 5; fig. 6) , or as extensions of 
rupture zones. Because of their obscurity relative to 
the ruptures, these zones of bending were not noted 
until after the preliminary field investigations had 
been concluded; the zones were mapped chiefly on 
the basis of distorted horizontal or vertical lines asso- 
ciated with structures such as curb lines, building 
walls, or pole lines. Distortion across these zones of 
bending includes formation of compressive welts as 
much as 23 inches high and lateral distortion of at 
least 0.05 percent over a zone 700 feet wide. The east 
end of the Z-shaped zone of bending at locality I 
may be related to lateral spreading of the adjacent 
hill; this interpretation is supported by the anoma- 
lously large westward displacement of the triangula- 
tion station on the hill (fig. 7) . 

Uplift, Tilting, and Horizontal Displacement 

Regional uplift and tilting affected an area of at 
least 75 square miles north of the rupture zone in 
the northern San Fernando Valley-southwestern San 
Gabriel Mountains area. The affected area extends 
from west of the San Fernando Reservoirs eastward 
to Big Tujunga Canyon and northward from the 
base of the foothills east of San Fernando to beyond 
the mouth of Pacoima Canyon (fig. 7) . Maximum 
uplift of about 7.5 feet occurred along an east- 



trending axis which coincides with the main rupture 
zone in San Fernando and continues eastward into 
the foothills about 0.5 mile north of their south mar- 
gin. Relative subsidence as great as 4 inches was 
measured south of the foothill rupture zone, gener- 
ally within the area bounded by the zero contour. 

In addition to the uplift, that part of the moun- 
tain block north of the San Fernando rupture zone 
was shifted generally southwestward between 2 and 4 
feet relative to the valley block south of the rupture 
zone (fig. 7) . 

Landslides 

Several destructive landslides occurred during the 
earthquake; the most significant of these occurred 
around the San Fernando Reservoirs and locally 
along the mountain front north of Sylmar. 

San Fernando Reservoir Landslides. — At the lower 
and larger dam of the San Fernando Reservoir com- 
plex (location J, fig. 5) , the embankment, parapet 
wall, dam crest for a length of about 1,400 feet, most 
of the upstream face, and part of the downstream 
slope slid into the reservoir (California Division of 
Safety of Dams 1971) . About 30 feet of dam height 
was lost, leaving a critically reduced freeboard of 
about 4 feet. Perhaps as much as 29,600 cubic yards 
of dam embankment was displaced; the resulting 
slide extended as much as 650 feet northward into 
the reservoir and covered an estimated 670 square 
yards of the floor. The landslide is attributed by 
Seed et al. (1971) to liquefaction of the hydraulic 
fill on the upstream side of the dam; these investiga- 
tors estimate that maximum accelerations of 40 to 50 
percent of g were attained in parts of the dam dur- 
ing the earthquake. 

The upper dam at the reservoir complex is about 
the same size as the lower dam, but it impounds a 
much smaller reservoir. The crest of the dam shifted 
as much as 5 feet downstream and settled about 3 
feet vertically during the earthquakes (California 
Division of Safety of Dams 1971) . 

Other smaller landslides and slumps affected the 
alluvial materials and fill around much of the mar- 
gins of the reservoirs; one scarp on the west shore of 
the lower reservoir is more than 0.5 mile lone: and 
was associated with a linear array of sand boils 
(Youd 1971, fig. 1). 

Juvenile Hall Landslide. — Another very destructive 
landslide extended northeastward from the northeast 



I IK 



San Fernando Earthquake <>\ 1971 



shore of the uppei reservoh (location K, hg. 5). 
Cracking, fissuring, and lateral moveraeni oi the 
ground surface downslope (generally toward thi 
ervoir) , associated with shaking resulting from the 
earthquake, severely damaged pits of a majoi elec- 
tricity converter station, ;i major juvenile detention 
facility, railroad trunklines, ;i majoi boulevard and 
an interstate freeway, and several pipelines and ea- 
nals. The affected area is tongue-shaped in plan and 
about 4,000 feet long and 900 feet wide at the down- 
slope, southwest margin. Topographs relief between 
the lake level at the toe and the land surface at the 
head was about 60 feet, an average effective gradient 
of about 1.5 percent. 

The landslide is hounded by relatively lineal 
/ones of discontinuous ruptures, locally en echelon 
(for details, see Volume III paper by Youd, 
"Ground Movements in Van Norman Lake Vicinity 
During San Fernando Earthquake"). Relative dis- 
placement across the /one ol ruptures bounding the 
north margin is consistently right lateral and as 
much as 2.8 feet; displacement across the south 
margin is consistently left lateral and as much as 1.9 
feet; vertical separations across fissures are as much 
as 7 inches; and fissures that intersei ted buildings at 
the detention facility are open as much as 15 inches. 

A number of postearthquake borings show that 
the area is underlain by silt and silty sand. This rela- 
tively fine-grained material was deposited in a topo- 
graphic depression at the confluence ol several small 
alluvial fans. 

The north margin of the slide is generally coinci- 
dent with the trace of the Olive View fault (fig. 2) 
as projected from the northeast; and although tec- 
tonic displacement of the ground surface along the 
fault trend is not evident on the basis of careful 
inspection, survey data indicate up to 0.40 foot of 
right-lateral displacement of the areas bounding the 
slide on the north and south (paper by Youd) . Ex- 
amination of predevelopment topography of this 
area (such as the 6-minute Sylmar quadrangle at 
1:24,000, 5-foot contour interval, 1935) clearly shows 
Grapevine Creek to be deflected about 500 feet in a 
right-lateral sense near the north boundary of the 
present failure, strongly suggesting that this is a re- 
curring process. The failure is considered to be re- 
newable in the event of another similar earthquake 
(Fallgren and Smith 1971, pp. 38-39) . 

Olive View Landslides. — Many of the older build- 
ings north and west of the new Olive View Hospital 



damaged severely by slop*- failure* in naiuial 
Hid filled ground at tin- base of the mountains north 
ol Svluiai (location I.. fig. V I lie y- lailui< 
curred on terraced slopes about 0.5 mile Ion; 
tending about 0.2 mile southward from the- ba 
tin hills and include 'uis along the ne-v. Foothill 
way, In addition landslides on the- west and 
south slopes ol tiic- small hill 0.2 mile- northeast ol 
the- new hospital sc\<-ic-l\ damaged the oldei build- 
ings there. In none ol these- *,iscs can the- ground 
failures be attributed to surface movement alon^ the 
Olive View fault, which trends northeastward be- 
tween the- tWO .ii I 

Camp Holton S/o/yr Failures. Destructive slope fail- 
ures affected both natural and anifieial materials at 
the Camp Kail Holton Juvenile facilities, 1.5 miles 
northeast ol the mouth <jI Little Tujunga Canyon 
(location X. fig. 5). A preexisting north-dipping 
fault in bedrock immediately northeast of the camp 
showed evidence ol movement involving about 6 
inches ol left-lateral displacement; this movement ex- 
tended westward into the gymnasium and accounts 
for the inejst severe structural damage at the camp. 
Slosson (1971 attributes this damage to shaking 
only and does not e iie the fault movement. 

Kagel Mountain Landslide. — A large landslide oc- 
curred on the north face of Kagel Memntain, 0.65 
mile clue cast of Paeoima Dam (location P, fig. 5). 
Individual fissures at the head ol the slide extend for 
more than 0.3 mile along the east and west shoulders 
ol the mountain, which is underlain by jointed, frac- 
tured, and foliated diorite and gneiss of the base- 
ment complex. Although fissures locally cut across 
the crest of the mountain, they are attributable to 
failure of the north slope rather than to tectonic 
movement (compare with Barrows et al. 1971, loca- 
tion 44) . 

Other Ground Failures. — Numerous other instances 
of ground failure, attributable to lurching, differen- 
tial settling, and related effects, caused considerable 
damage in marginal areas of the San Fernando Val- 
ley. Chief of these is the area west of the San Fer- 
nando Reservoir complex (location Q, fig. 5) , gener- 
ally along the trend of the Olive View fault, where 
a number of destructive fissures formed on gentle 
slopes in alluvial and fill materials. These fissures 
generally trend subparallel to the contours of local 
slopes and are not directly attributable to surface dis- 
placement on the fault. 



Effects of Earthquake as Related to Geology 149 



Shattered Ground 

Numerous examples of closely spaced, randomly 
oriented fissures are present in the soil on the tops of 
many ridges around the west, north, and east mar- 
gins of San Fernando Valley (Barrows et al. 1971). 
The Assuring produced large, tilted, and overturned 
clods and blocks of soil in areas of finely pulverized 
soil. The effect is especially well developed just 
above the lower branch of the Santa Susana thrust in 
the foothills west of the San Fernando Reservoirs, 
along the mountain front north of Sylmar, and in 
the foothills east of San Fernando. Barrows et al. 
(1971) associate the shattering with especially angu- 
lar topography and with ridges underlain by sand- 



stone and conglomerate with a relatively thin soil 
cover. A relatively dense concentration of the shat- 
tering is associated with the axis of the Little Tu- 
junga syncline, which trends northwest from Little 
Tujunga Canyon about 2 miles northeast of its 
mouth, and which is underlain by very steeply dip- 
ping sandstone and conglomerate beds. 

Structural Damage 

The plots of damage (figs. 8 and 9) are intended 
to represent primarily the areal distribution and 
density of significant damage to structures; they are 
based on field observations and on lists supplied by 
the cities of Los Angeles and San Fernando, Los An- 



1 18°30' 



II 8° 22' 30" 



34' 
22'30' 




34< 
15 







PsX 



H-Hospltal or nursing home 
S- School 

-Pre-Field Act school 
severely damaged 

"-Apartment 01 dormitory 

■ -House or commercial building 

D-Dom 

F-Freeway overpass 

Lj-Quaternory deposits 

Tectonic ruptures 
Boundary of epicentral areo 







2 I 

I I L 




Figure 8. — Map of northern San Fernando Valley area, showing distribution of structural damage 
relative to geology. Base from Wentworth et al. (1971). 



150 San Fernando Earthquake of 1971 



' 






x x x. 



/ 






SANTA 

SUSAN 



1/5. 






%& -n 



. 




• imorphlc or p] 

X Damaged school building 

iiool building damaged 
beyond economi'. repair 

. Damaged house, apartment, or 
commercial building 



• • • •. .... .V 



• ••v 



MONICA MIS x j*.' 




• X 



.. * 



•• . x. .©. • 

.x +•&&•• 

• • • 



x» X 



SANTA 
MONICA 



x • Lt> S 
e x 

• x 

• X 



ANGELES 



BASIN 



MILES 






Figure 9. — Map of San Fernando Valley-Los Angeles Basin area, showing distribution 
of structural damage relative to geology. Base same as figure 2. 



geles City School District, and Los Angeles County. None of the lists indicate the age or type of con- 
Only one of these lists separates structural from ar- struction. Thus, it was impossible to normalize the 
chitectural damage; others give only the estimated data satisfactorily; instead, the plots include all indi- 
cost of repairs to the structures or identify only those vidual structures intended for some degree of occu- 
structures that were posted as unsafe for occupancy, pancy for which repairs were estimated to equal or 



Effects of Earthquake as Related to Geology 151 



to exceed $2,000. Eight pre-1933 school buildings 
that were damaged beyond economic repair are dif- 
ferentiated; the plots also include the wood frame 
dwellings in the northern San Fernando Valley that 
were examined and plotted by Steinbrugge et al. 
(1971, fig. 16). 

Estimates of Average Loss. — The loss caused by the 
moderate San Fernando earthquake to private 
homes is of interest because the geology of the north- 
ern San Fernando Valley area approximates that 
along the entire northern margin of the Los Angeles 
Basin. 

Steinbrugge et al. (1971) summarize data on 
earthquake-related damage to 12,037 wood frame 
dwellings in the heavily shaken area of San Fer- 
nando Valley north of the rupture zone. The average 
loss of each dwelling, based on estimates of preearth- 
quake market value and repair costs, is 6.6 percent. 
As based on the values of the Los Angeles County 
Assessor and the estimated losses for 1,088 dwellings 
uniformly distributed in the same area, the average 
loss was 21.5 percent (Steinbrugge et al. 1971). In 
June 1971, the Small Business Administration had 
approved loans for earthquake repairs to 11,815 
dwellings (type not specified) in the northern San 
Fernando Valley area (U.S. Congress 1971, p. 41). 
The loans averaged $3,860, representing 24.6 percent 
of the $15,700 average value (as based on the figures 
of Steinbrugge et al. 1971) or 27.2 percent of the av- 
erage value (as based on the figures of the Los Ange- 
les County Assessor). Steinbrugge et al. (1971, fig. 
24) also found that 25 percent of their sample had 
losses exceeding 5 percent of the preearthquake mar- 
ket value, 14 percent had losses exceeding 10 percent 
of their value, and about 2 percent (217) had losses 
exceeding 50 percent. The Small Business Adminis- 
tration reported in June 1971 (U.S. Congress 1971, 
p. 418) that more than 1,200 homes were damaged 
in excess of $17,000 — more than the average value of 
dwellings in the area. 

Distribution of Damage. — Severe damage to modern 
structures was restricted to the Sylmar-San Fernando- 
Pacoima area — that part of northern San Fernando 
Valley north of the rupture zone. Within that area, 
it was particularly intense along the rupture zone 
in the city of San Fernando and along the mountain- 
front belt of severe shaking north of Sylmar (fig. 8) . 
Although the zone of tectonic ruptures is as much as 
660 feet wide in the city of San Fernando, the most 



damaging deformation — vertical and lateral displace- 
ment and compressive horizontal shortening normal 
to the trend of the zone — occurred chiefly within a 
band about 200 feet wide along the south margin of 
the zone. The northern part of the zone shows chiefly 
extensional features: open cracks and small fissures 
with relatively small vertical displacements. 

The mountain-front belt of intense shaking dam- 
age north of Sylmar is about 0.75 mile wide and ex- 
tends at least 7 miles from the alluvial area west of 
the Upper San Fernando Reservoir eastward to Pa- 
coima Dam. This belt includes the area of landslid- 
ing around the east end of the Upper San Fernando 
Reservoir, the Olive View medical facilities, the Vet- 
erans Administration Hospital facilities, and several 
intervening tracts of houses. Only one short segment 
of presumed tectonic rupturing occurred in this belt 
(about 0.5 mile east of the Veterans Administration 
Hospital, near the mouth of Pacoima Canyon — see 
location H, fig. 5) ; although the fault intersected 
some structures, the most severe damage along its 
trend appears to be the result of shaking. In addi- 
tion, failure caused by landsliding was extensive and 
very damaging at places along the belt, as at the San 
Fernando Valley Juvenile Facility and the older parts 
of the Olive View facility. 

No evidence of significant ground failure has been 
noted in the failures of the new hospital and psychi- 
atric units at Olive View, where vertical and lateral 
accelerations of the ground are inferred to have ex- 
ceeded 40 percent of g (Structural Engineers Asso- 
ciation of Southern California 1971, Slosson 1971, 
and Frazier et al. 1971, pp. 175-180) . The San Fer- 
nando Veterans Administration Hospital complex is 
located in the mountain-front belt about 1 mile 
southwest of Pacoima Dam; the complex includes a 
number of both pre-1933 and post- 1933 buildings. 
The older buildings collapsed or were damaged se- 
verely, whereas the post- 1933 buildings suffered no 
severe structural damage (Frazier et al. 1971) . 

Several tracts of new wood frame dwellings, one 
story, one and two story, or two story, are located in 
the mountain-front belt east of the Olive View medi- 
cal facility. One of the most severely damaged was a 
tract of uncompleted one-story houses just east of the 
Veterans Administration facility, near the mouth of 
Pacoima Canyon. In this tract, a number of houses 
that were framed, but not completely walled, col- 
lapsed. In tracts between the Olive View and Veter- 
ans Administration facilities, the most severe damage 



152 San Fernando Earthquake of 1971 



was sustained l>y combination one- and two-story 
houses in which the lower story ol the two-story part 
collapsed because ol inadequate lateral bracing. In 

none ol these cases was ground lailme a significant 

cause ol damage. 

Effects o) Deformation, I he effects ol surface defor- 
mation include the following: Vertical displacements 
caused tilting and fracturing of floors, foundations, 
and pavements; and lateral displacements caused 
shearing, buckling, and stretching ol pipelines, pave- 
ments, and foundations so thai a pipeline 01 side- 
walk that was buckled in compression at one point 
was commonly broken in tension at another. The 
shortening component caused buckling ol founda- 
tions, pavements, and pipelines. In other instances, 
the shortening was expressed as slippage between the 
structure and the adjoining ground so that pipelines 
were thrust over curbs and buildings seemingly slid 
over the ground surface. In one instance, a building 
was jammed into an adjacent building formerly sepa- 
rated by a 6-inch gap; after the earthquake, the two 
buildings overlapped about 1 foot (Frazier et al. 
1971, pp. 233-235). Those structures that were in- 
tersected by the ruptures were subjected to vertical 
and lateral displacements of more than 3 feet and 
compressive horizontal shortening of as much as 2 
feet. These displacements may have been imposed at 
rates of 3 fps (feet per second) or greater. 1 

Correlation and Implications. — The distribution of 
damage shows a strong correlation with: 1) the rela- 
tively narrow zone of tectonic ruptures in the San 
Fernando area; 2) the south-facing mountain front 
of the San Gabriel Mountains north of Sylmar, ex- 
tending southeastward from San Fernando to Pasa- 
dena; and 3) the boundaries of alluviated areas (Qi 
and G\, figs. 8 and 9) . On a relative basis, the 
amount of damage caused by the zone of tectonic 
ruptures was small, but the degree of damage was 
large. 

The most severe damage was sustained by struc- 



1 The peak velocity of horizontal ground movement derived from 
analysis of the Pacoima Dam accelerogram, recorded on jointed 
crystalline basement rocks, was 3.77 fps; the peak rate of vertical 
movement was about one-half of that amount (Trifunac and Hud- 
son 1971) . The velocity of displacement of alluvium during normal 
faulting associated with buried nuclear explosions in Nevada ranged 
upward from about the same value, 3.3 fps. In contrast to these 
rates are the velocities of propagation of ruptures along the ground 
surface during the nuclear tests, more than 2 km (6,560 ft) per 
second, comparable to expected shear-wave velocities in alluvium 
(McKeown and Dickey 1969) . 



tines ol all types and ages aloir^ the mountain-front 
helt north ''I S'.linat where the intensity ol thai 
local ded 40 perccni of g. Accelerations 

not measured along the mountain front between I'a- 
coima Dam and Pasadena, but horizontal accelera- 
tions as high as 24 percent of g were measured at 
Sic ] i, i Madre, 'l'> miles southeast ol the < 
(fig. 4). Although the alluvium is very thin in the 

Sylmai aica (fig. 3), that aiea overlies the fault sur- 
face and was intensely shaken, with accelerations of 
30 percent ol g and greater. The intensity ol shaking 
was somewhat diminished in the main part ol San 
Fernando Valley south ol the rupture /'me, where al- 
luvium is relatively thick, and in the northern part 
ol the I. os \n^e les basin. These effects emphasize 
the conclusion ol Steinbrugge et al. (1971, p. 11) 
that mountain-front /ones, known to be associated 
with geologically voting faults such as the Sierra 
Madre, are especially hazardous areas in terms of 
seismic shaking and potential surface faulting. 

PREDICTING THE FAULTIM. 

Barrows et al. (1971) report the results of shallow 
trenching across the rupture zone at a number of dif- 
ferent localities. In only one of eight trenches dug 
across the tectonic ruptures in alluvial deposits could 
the causative fault be recognized in unconsolidated 
gravels; this result supports the judgment of Jen- 
nings and Housner (1971, p. 491) that the location 
of individual surface ruptures could not, in general, 
have been predicted precisely enough so that occu- 
pants of specific buildings could be warned of the 
hazard. (Where the ruptures involved consolidated 
materials, the fault surface was identified readily in 
the trench walls.) However, the zone of surface rup- 
tures coincides, in general, with a preexisting topo- 
graphic scarp and a ground water impediment, both 
of which indicate geologically young, recurring fault- 
ing along this part of the valley floor. Thus, the gen- 
eral position of the 1971 rupture zone could have 
been determined had a specific study been made. 

The 1971 tectonic ruptures have been mapped at 
scales suitable for future identification of their loca- 
tion to within 50 feet, the width of small city lot 
(Barrows et al. 1971; Kamb et al. 1971, fig. 3; and 
the U.S. Geological Survey Staff 1971, fig. 2). This 
record should surely serve as sufficient warning of fu- 
ture risk to those occupying buildings within the 
zone, even if more detailed mapping is not available. 






Effects of Earthquake as Related to Geology 153 



The distribution of the greatest deformation across a 
zone about 200 feet wide suggests that the precise lo- 
cation of individual ruptures may not be as signifi- 
cant for engineering purposes as identification and 
proper land-use zoning of the area within which rup- 
turing may recur. 

There is little doubt that the fault along which 
the February 1971 tectonic ruptures occurred could 
have been recognized beforehand had sufficiently de- 
tailed studies been made. However, no study specifi- 
cally directed toward locating the fault or its degree 
of activity had been made; this is not surprising be- 
cause in only very recent years have geologists begun 
to evaluate the potential activity of faults that have 
no record of historic rupture. However, preexisting 
evidence, such as the ground water impediment and 
topographic scarps, could have led to specific investi- 
gation and to a reasonable assessment of the degree 
of activity (e.g., Wentworth et al. 1970) . In addition, 
analysis of topographic expression of the faults and 
relevant literature (Oakeshott 1958, Hill 1954, Meri- 
field 1958, and Proctor 1970) could have led to pre- 
diction of the type of movement to be expected on 
the fault. 

CONCLUSIONS 

The San Fernando earthquake was unique in sev- 
eral respects: It was the first in historic time to form 
tectonic ruptures in the Los Angeles metropolitan 
area; the geometry of the causative fault is such that 
it underlies part of the urbanized area at shallow 
depths, thus accounting, in part, for the relatively in- 
tense effects in that area; and these effects included 
the strongest ground motions ever recorded and were 
relatively well recorded over a large part of the 
northern Los Angeles Basin. 

At magnitude 6.4, the earthquake was significantly 
smaller than the 1857 Fort Tejon earthquake (mag- 
nitude 8 + ), caused by right-lateral strike slip and 
surface rupturing on the San Andreas fault just 
north of the San Gabriel Mountains, as well as the 
1952 Kern County earthquake (magnitude 7.7) , 
caused by left-oblique reverse slip and surface rup- 
turing on the White Wolf fatdt. These much larger 
earthquakes and much longer rupture zones resulted 
from the same stress system that produced the San 
Fernando earthquake, which thus should be viewed 
as only the lower limit to be expected from this sys- 
tem. 



Damaging effects of the earthquake can be corre- 
lated with the narrow zone of tectonic ruptures, with 
the area of relatively intense shaking between the 
rupture zone and the epicenter of the main shock, 
and with boundaries between unconsolidated al- 
luvial materials and harder rocks. Although evidence 
of geologically young movement along the San Fer- 
nando fault was available, it had not been recog- 
nized or appreciated. Faults not now recognized as 
active in this area (south and southeast of the "great 
bend" of the San Andreas) should be examined for 
such evidence. 

REFERENCES 

Allen, Clarence R., Engen, G.R., Hanks, Thomas C, Nord- 
quist, f.M., and Thatcher, W.R., "Main Shock and Larger 
Aftershocks of the San Fernando Earthquake, February 9 
Through March 1, 1971," The San Fernando, California. 
Earthquake of February 9, 1971, Geological Survey Profes- 
sional Paper 733, U.S. Geological Survey and the National 
Oceanic and Atmospheric Administration, U.S. Department 
of the Interior and U.S. Department of Commerce, Wash- 
ington, D.C.. 1971, pp. 17-20. 

Barrows, A.G., Kahle, I.E., Weber, F.H., Jr., and Saul, R.B., 
Map of Surface Breaks Resulting From the San Fernando, 
California, Earthquake of February 9, 1071, Preliminary Re- 
port II, Plate I, California Division of Mines and Geology, 
Sacramento, 1971, scale 1:24,000. 

California Division of Safety of Dams, "Effects of the San 
Fernando Earthquake on the Van Norman Reservoir Com- 
plex," California Department of Water Resources Interim 
Report, Sacramento, May 1971, 27 pp. and 5 pi. 

California State Water Rights Board. "City of Los Angeles vs. 
City of San Fernando, et al.," San Fernando J'alley Refer- 
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Court, Los Angeles County, Calif., July 1962. 

Corbato, Charles E., "Bouguer Gravity Anomalies of the San 
Fernando Valley, California." California University Publi- 
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California Press, Berkeley, Nov. 1963, pp. 1-32. 

Fallgren, Richard B., and Smith, Jay L., "Geologic and Soil 
Investigation, San Fernando Valley Juvenile Hall, Sylmar, 
California," for the Los Angeles County Engineer by 
FUGRO, Inc.. Long Beach, Calif., Sept. 20, 1971, 45 pp. 
and 2 pi. (unpublished report) . 

Frazier, G.A., Wood, J.H., and Housner, G.W., "Earthquake 
Damage to Buildings," Earthquake Engineering Research 
Laboratory Report EERL 71-02, California Institute of 
Technology. Pasadena, June 1971, pp. 140-298. 

Hill, M.L., "Tectonics of Faulting in Southern California," 
California Division of Mines Bulletin 170, Sept. 1954, pp. 
5-14. 

Hudson, Donald E., "Strong-Motion Accelerogram Processing," 
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Earthquake of February 9, 1971, Division of Engineering 
and Applied Science, Earthquake Engineering Research 



154 San Fernando Earthquake of 1971 



Laboratory, California Institute oi Technology, Pasadena, 
Sept. 1971, pp. i r >7 204 (sec table I, pp. 165 181). 

Jennings, P.C., and Housner, G.W., "Conclusions and Recom 
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Pasadena, June 1971, pp. 471 499. 

Jennings, C.W., and Strand, R.G., Geologii Map <>\ California, 
()lnf P. Jenkins Edition, I <>s Angeles Sheet, California 
Division of Mines and Geology, Sacramento, 1969, scale 
1:250,000. 

Kami), Barclay, Silver, L.T., Abrams, M.J., Carter, B.A., foi 
dan, Thomas H., and Minster, |. Bernard, "Pattern of Fault- 
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U.S. Geological Survej and the National Oceanu and \t 
mospheri< Administration, U.S. Department oi tin- fnterioi 
and U.S. Department oi Commerce, Washington, D.C., 
1971, pp. 41-54. 

McKeown, F.A., and Dickey, I). I)., "Fault Displacements and 
Motion Related to Nuclear Explosions," Bulletin of the 
Seismological Society of America, Vol. 59, No. 6, Dec. 1969, 
pp. 2253-2270. 

Merifield, P.M., "Geology of a Portion of the Southwestern 
San Gabriel Mountains, San Fernando and Oat Mountain 
Quadrangles, Los Angeles County, California," M.A. thesis, 
University of California, Los Angeles, 1958, 61 pp. 

Oakeshott, Gordon B., "Geology and Mineral Deposits ol San 
Fernando Quadrangle, Los Angeles County, California," 
California Division of Mines Bulletin 172. Feb. 1958, 147 
pp. (see plate 1, scale 1:62,500, in back pocket). 

Oliver, H.W., Robbins, S.I... Grannell, R.B., Alewine, R.W., 
and Biehler, Shawn, "Surface and Subsurface Movements 
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lished). 

Proctor, R.J. (Compiler), "Geologic Map and Sections Along 
the 4.4-Mile Sunland runnel." B-20262, Metropolitan 
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1970 (unpublished map. scale 1:12,000). 

Scott, Nina H., "Preliminary Report on Felt Area and In- 
tensity," The San Fernando, California, Earthquake of Feb- 
ruary 9, 197 1, Geological Survey Professional Paper 733, U.S. 
Geological Survey and the National Oceanic and Atmos- 
pheric Administration, U.S. Department of the Interior and 
U.S. Department of Commerce, Washington, D.C., 1971, 
pp. 153-154. 

Scott, R.F., "Preliminary Soil Engineering Report." Engineer- 
ing Features of the San Fernando Earthquake of February 9, 
1971, Earthquake Engineering Research Laboratory Report 
EERL 71-02, California Institute of Technology, Pasadena, 
June 1971, pp. 299-331. 

Seed, H.B., Lee, K.L., and Idriss, I.M., "Appendix B— Pre- 
liminary Report on Lower San Fernando Dam Slide During 
the San Fernando Earthquake of February 9, 1971," Effects 
of the San Fernando Earthquake on the Van Norman Reser- 



Complex, California Division of Saletv of D. 
memo, Maj 1971, 13 \>\>. and 15 pL 

Slosson, James E., "Engineering Gcoh 
nando Valley Juvenile Hal] Exhibit D," Report 

Hospital, Structural Engii on of Vji>' 

California Los Angeles, May 2';, 1971, i pp. 

Steinbrugge, Karl V , Schadei 1 1 Biggie tone II'. and 
Wins f. \ Sun Fernando Earthquake Fel 
Pacific Fire Rating bin can San Francisco Calif., 1971, 9 

Structural I ngineers V*so< iation of Southern California, Report 
on Olive I •■ ■ Hospital, Los tngeles Ma\ 25, 1971 40 pp. 

Trifunac, Mihailo I) and Hudson, Donald E. "Anal, 
tin I'.Koima Dam Accelero California, 

Earthquake ol 1971," Bulletin of the Seismological So 
Of .line,,, a, Vol. 61, No 5 Oct. 1971. pp. 1393-1411. 

IS Congress. Seriate Committee on Public Worl 

mental Response to the California Earthquake DiiOSU 

February 1971, Serial No. 92-H22, U.S. 92d Congress, 1st 

Session. Washington. D.C., 1971, 985 pp. 

U.S. Geological Survey Stall. Surface Faulting." The San Fer- 
nando, California, Earthquake of February 9, 1971, Geologi- 
cal Survey Professional Paper 733. U.S. Geological Survey 
and the National Oceanic and Atmospheric Administration, 
U.S. Department of the Interior and US. Department of 
Commerce, Washington. D.C., 1971, pp. 55-7 

W'entworth, Carl M.. Ycrkes. R.F.. and Allen, Clarence R., 
"Geologic Setting and Activity of Faults in the San Fer- 
nando Area. California," The San Fernando, California, 
Earthquake of Februaiy 9, 1971, Geological Survey Pro- 
fessional Paper 733, U.S. ecological Survey and the Na- 
tional Oceanic and Atmospheric Administration, U.S. De- 
partment of the Interior and U.S. Department of Com- 
merce, Washington, D.C., 1971, pp. 6-16. 

W'entworth. Carl M.. Zionv. J. I., and Buchanan. J.M.. Pre- 
liminary Geologic Environmental Map of the Greater Los 
Angeles Area. California, Plate 1," US. Atomic Energy Com- 
mission TID-25363, Technical Information Division, Oak 
Ridge, Tenn., 1970, scale 1:250,000. 

Wesson. R.L.. Lee. W.H.K.. and Gibbs. J.F.. "Aftershocks 
of the Earthquake," The San Fernando, California, Earth- 
quake of February 9, 1971. Geological Survey Profes- 
sional Paper 733, U.S. Geological Survey and the National 
Oceanic and Atmospheric Administration. U.S. Department 
of the Interior and U.S. Department of Commerce, Wash- 
ington, D.C.. 1971, pp. 24-29. 

Youd. T. Leslie, "Landsliding in the Vicinity of the Van 
Norman Lakes," The San Fernando, California, Earthquake 
of February 9, 1971, Geological Survey Professional Paper 
733, U.S. Geological Survey and the National Oceanic 
and Atmospheric Administration, L T .S. Department of the 
Interior and U.S. Department of Commerce, Washington, 
D.C., 1971, pp. 105-109. 

Youd, T. Leslie, and Castle, R.O., "Borrego Mountain Earth- 
quake of April 8, 1968," Proceedings Paper 7396, Journal of 
Soil Mechanics and Foundations Division, Vol. 96. No. 
SM 4, July 1970, pp. 1201-1219. 



Subsurface Geology of 

Portions of San Fernando Valley 

and Los Angeles Basin 



CONTENTS 



155 Introduction 

155 Regional Geology 

155 General Geology of San Fernando 

Valley Area 
159 General Geology of Los Angeles 

Basin 

161 Stratigraphy of San Fernando Valley 

Area 

162 Stratigraphy of Los Angeles Basin 

163 References 

164 Bibliography 



J. A. JOHNSON 

Geologist 

C. M. DUKE 

Professor of Engineering 

University of California at Los Angeles 
Los Angeles, Calif. 



INTRODUCTION 

The regional geologic setting of the San Fernando 
Valley area and the Los Angeles Basin and a detailed 
representation of subsurface geological conditions at 
selected locations of instruments which recorded the 
main shock and certain aftershocks of the San Fer- 
nando earthquake are presented in this paper. Fig- 
ure 1 is a generalized geologic map showing the loca- 
tions of geologic cross sections A-A' (fig. 2) and 
B-B' and C-C' (fig. 3) . Tables 1 and 2 are general- 
ized geologic columns for the San Fernando Valley 
and Los Angeles Basin, respectively. 

The general geologic map was designed to give a 
survey of the major rock types in the area studied 
(basement rocks, sedimentary rocks, and recent al- 
luvial materials) and their relationship to topo- 
graphic and geologic features. The three geologic 
cross sections are of interest for studies of earthquake 
ground motion. See the paper by Duke et al., 
"Subsurface Site Conditions in the San Fernando 
Earthquake Area," in the section on Soils and Foun- 
dations, Volume I, for the engineering aspects of the 
Deep Subsurface Models identified in figures 2 and 
3. Areas of little information are interpretive, and 
the conventional symbols were used to indicate the 
reliability of the information. 

REGIONAL GEOLOGY 

General Geology of San Fernando Valley Area 

The San Fernando Valley is a broad, fairly flat 
plain bounded on the north by the San Gabriel and 
Santa Susana Mountains, on the west by the Simi 
Hills, on the south by the Santa Monica Mountains, 
and on the east by the Verdugo Mountains. See gen- 
eralized geologic map (fig. 1) . 



155 



156 San Fernando Earthquake of 1971 



F^^ 




Fault, dashed where approximately 
*^^ located or concealed 

pr Thrust Fault, barbs on upper plate; 

dashed where approximately located 

•^mmm Surface Break, February 9, 1971 

_ A 

O Deep Subsurface Models 



Cross Section Line 



Geology modified from California Division 
of Mines and Geology map sheets of Los 
Angeles, San Bernardino, Long Beach, 
and Santa Ana by J. A. Johnson 



Figure 1. — Generalized geologic map of Los Angeles area. Lines A— A', B-B f , and C-C 
are locations of geologic rtoss sections shown in figures 2 and 3. 



Subsurface Geology of Earthquake Area 157 




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I r *K San Fernando Earthquake <>\ 1971 



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Subsurface Geology of Earthquake Area 159 



Structurally, the valley is a faulted series of folds 
(Bailey and Jahns 1954, cross section A-A') that 
broadens and deepens to the east where it is trun- 
cated by the upfaulted southwest front of the Ver- 
dugo Mountains. To the north is a smaller fold, 
known as the Little Tujunga syncline (Oakeshott 
1958) , that extends along the southern margin of the 
San Gabriel Mountains. The northern limb of this 
fold is truncated by the San Gabriel Mountains 
(cross section B-B') . The southern border of the 
valley is underlain by the north-dipping sedimentary 
formations that cap the Santa Monica Mountains 
(cross section A-A') . 

The sediments underlying the valley at their deep- 
est point include some 15,000 feet (Corbato 1963) 
of broadly folded and faulted Cenozoic and Mesozoic 
(?) rocks that unconformably rest on basement com- 
plex (table 1) . Quaternary materials in the form of 
stream-deposited, coalescing alluvial fans and terrace 
deposits blanket most of the floor of the valley. 

The southern margin of the valley is bounded by 
the east-west trending Santa Monica Mountains. 
Structurally, the mountainous area east of Topanga 
Canyon is a large, complexly faulted anticline which 
plunges to the west with basement rocks exposed to 
the east (cross section A-A') . Rocks of the area in- 
clude a wide variety of coarsely crystalline plutonic 
rocks, other intrusives and pyroclastic rocks, meta- 
morphic schists and slates, and a sequence of sedi- 
mentary rocks (Hoots 1931). 

The San Gabriel Mountains, which border the val- 
ley to the north, are bounded on all sides by major 
faults. The series of faults, along the northern mar- 
gin of the valley or the southern margin of the San 
Gabriel Mountains, are north-dipping thrust faults 
which offset rocks as young as Quaternary and in- 
clude the fault that broke the surface on February 9, 
1971 (cross section B-B') . 

The rocks within the San Gabriel Mountains con- 
sist of late Mesozoic plutonic rocks and a complex 
series of older plutonic, metasedimentary, and meta- 
volcanic rocks. 

The Simi Hills are a faulted and elevated block of 
massive Upper Cretaceous sandstones and thinly bed- 
ded shales, overlain by lesser amounts of Eocene and 
Miocene marine sandstones and conglomerates. To 
the north and east of the Simi Hills are the Santa 
Susana Mountains, a complexly folded and faulted 
series of Miocene marine sandstones, conglomerates, 
and diatomaceous shales. 



The extreme eastern end of the valley is bounded 
by an uplifted block of metamorphic and granitic 
rocks. This block, known as the Verdugo Mountains, 
is separated from the valley by the Verdugo fault 
and from the La Crescenta area, to the east, by the 
La Crescenta Valley fault. 

General Geology of Los Angeles Basin 

The Los Angeles Basin, as described in this report, 
is a structurally complex region bounded on the 
north by the Santa Monica Mountains and the Ely- 
sian, Repetto, and Puente Hills. The southern 
boundary is made up of the Palos Verdes Hills and 
the Pacific Ocean. Although the basin extends be- 
neath the Pacific Ocean, this part will not be in- 
cluded in the discussion. 

The present topography of the basin is a low-lying 
surface which, except for a series of hills along the 
Newport-Inglewood uplift and the Palos Verdes 
Hills, slopes gently toward the ocean. The subsurface 
geology is not as simple as the topography and, 
therefore, has been broken up into several subbasins 
or "blocks" on the bases of rock type (table 2) and 
a series of major faults that cross the region (Yerkes 
et al. 1965) . This report is concerned only with 
Yerkes' "Southwestern Block," the northwestern part 
of the "Central Block," and the westernmost portion 
of the "Northeastern Block" (Yerkes et al. 1965, fig. 
3, p. A5) . See general geologic map in figure 1. 

The surface of the "Southwestern Block" is a low 
flat plain that extends from the Santa Monica- 
Hollywood fault zone (cross section A-A') south to 
Long Beach, with little topographic relief except for 
the Palos Verdes Hills. The area to the east is 
bounded by the Newport-Inglewood fault zone. 

Based on oil well information and exposure in the 
Palos Verdes Hills, the basement complex of the 
"Southwestern Block" probably is composed entirely 
of Catalina schist (Schoellhamer and Woodford 
1951). The overlying rocks are a thick section of 
middle Miocene to Recent marine sediments, which 
locally includes Miocene intrusives. 

Structurally, this block consists of two major 
northwest-trending anticlinal arches (Yerkes et al. 
1965) in basement rocks north of the Palos Verdes 
Hills. To the south and underlying the Palos Verdes 
Hills is a doubly plunging anticline paralleling these 
major structures. 

The area studied in the "Central" and "Northeast- 
ern" Blocks is south of the Hollywood and Raymond 



160 San Fernando Earthquake of 1971 

Table I -(.'ru-ralizrd gfiptogU (olumn-San I ' rrruindo Vtttet 



Quater- 
nary 



Tertiary 



Age 



Recent 



Upper Pleistocene 



Middle Pleistcn ene 



Lower Pleistocene- 



Pliocene 



Upper 

Middle 



Lower 



Upper Miocene 



Middle to lower Miocene 



Middle Eocene 



Lower Eocene to Paleocene 
(?) 



I onnation name 



Alluvium 



Oldei alluvium and terrace 
deposits 



\'.k onna Formation 



Saugus Formation 



Fernando 
Forma- 
tion (?) 



Pu o I Oi mation 
(Sunshine 
Ranch; 



Repetto Forma- 
tion (Towsley) 



Modelo Formation 



Topanga Formation 



Domengine Formation 



Martinez Formation 



Lhli',. 



Clay, nit, and land <o the wen end of the /alley; coarser 
material ravel, and boul - • 

portion of the valley. 



Well-graded, poorly a I, angulat-to-subar., 

Eanglomerate and trrrar <- giavels. 



l<i-ddish-hrown, well-graded, and slightly (aided COBgk 
and (angioma 



Well-graded, loosely consolidated, nonmanr- 

and < oarsr-i/rainrd sandstone beds, with generally liner 
interbedded marine sediments toward the v>ett end of the 
valley. 



Nonmarine sandstone, mudstone, and tonjdoinerate which 
grade into older sediments, consisting of marine sand 
siltstone, and conglomerate. 



Marine sandstone, conglomerate, siltstone, and shale. 



Marine fine-to-coarse-grained sandstone and conglomerate, 
interbedded with diatomaceous shales. 



Coarse-grained continental and marine sandstone and con- 
glomerate beds, interbedded with basaltic lava flows. 



Massive marine sandstone and conglomerates. 



Coarse sandstone, interbedded with dark shales and pebble 
conglomerate. 



Upper Cretaceous 



Chico Formation 



Massive marine sandstones, coarse conglomerates, and inter- 
mixed shale beds. 



Pre-Cretaceous 
to Precambrian 



Basement 
com- 
plex 



Santa Monica 
Slate, Jurassic (?) 



Mendenhall 
Gneiss 



Granitic and metamorphic rocks. 
Black slates with schist facies. 

Quartz-feldspar gneiss intruded by gabbroic rocks. 






Hill fault zones, east of the Newport-Inglewood 
uplift, and west of the San Gabriel River (fig. 1 and 
cross section C-C) . 

Topographically, the region includes the Elysian 
and Repetto Hills, a low-lying plain to the south, 
and the northwest-trending hills that extend south 
from Beverly Hills along the Newport-Inglewood 
fault zone. 

The basement complex of the "Central" and 



"Northeastern" Blocks, which consists of Mesozoic 
metasedimentary rocks, is overlain by up to 32,000 
feet of Late Cretaceous to Pleistocene marine-nonma- 
rine sediments interbedded with middle Miocene vol- 
canics (Yerkes et al. 1965) . Locally, the area is blan- 
keted by a thin layer of alluvial and older alluvial 
materials. 

Structurally, this area is dominated by an asvm- 
metrical, doubly plunging, synclinal trough that 



Subsurface Geology of Earthquake Area 161 
Table 2.— Generalized geologic column— Los Angeles Basin 



Age 


Formation name 


Lithologic description 




Recent 


Alluvium 


Sand, silt, gravels, and dune sand. 


Quater- 
nary 


Upper Pleistocene 


Terrace and older alluvium 


Marine and nonmarine silt, sand, and gravel-forming terrace 
deposits. 




Lower Pleistocene 


San Pedro Formation 


Silt, sand, gravel, and clay. 




Pliocene 


Upper Pliocene 


Fernando 
Forma- 
tion (?) 


Pico Formation 


Tan-to-brown conglomerate, sandstone, and siltstone. 




Lower Pliocene 


Repetto Forma- 
tion 


' 


Tertiary 


Miocene 


Upper Miocene 


Puente, Monterey (Palos 
Verdes Hills), and Modelo 
Formation 


Siltstone and shale, well-bedded; coarse-grained sandstone 

and conglomerate. 
Palos Verdes Hills — mudstone and diatomaceous shale with 

siltstone, sandstone, limestone, and conglomerate. 




Middle and 

lower(?) Miocene 


Topanga Formation 


Coarse-grained, well-bedded sandstone; massive conglomerate 
and siltstone with interbedded sandstone. 




Oligocene 

Eocene 

Paleocene 


Vaqueros, Sespe, Santiago, 
and Silverado Formations 


Not present in area of study. 






Base- 
ment 
com- 
plex 


West- 
ern 
com- 
plex 


Catalina 
Schist, 
Jurassic 

(?) 


Fine-grained chlorite quartz schist and blue glaucophane- 
bearing schist. 




Upper Cretaceous 


East- 
ern 
com- 
plex 




Granitic intrusives. 




Upper Jurassic 




Volcanics. 




Triassic 








Metasedimentary schists. 



trends northwest. The structural relief of the base- 
ment rocks between the ends and central portion of 
the trough varies vertically between 15,000 and 
18,000 feet. 

The Elysian-Repetto Hills area is very complex 
because of its location at the intersection of the east- 
west-trending Hollywood fault system and the north- 
west-trending faults which may be a part of the 
Whittier fault system (Lamar 1970) . This complex 
fault pattern has caused rapid local changes in the 
lithology and thickness of Miocene formations in the 
area (cross section C-C) . 

STRATIGRAPHY OF SAN FERNANDO 
VALLEY AREA 

Basement Rocks. — The basement complex of the San 



Fernando Valley area is a group of pre-Cretaceous 
crystalline and metamorphic rocks, exposed in and 
comprising the main mass of the San Gabriel and 
Verdugo Mountains to the north of the valley and 
the eastern portion of the Santa Monica Mountains 
to the south. The subsurface distribution of pre-Cre- 
taceous basement rocks below the San Fernando Val- 
ley is unknown as to type and extent. 

Basement rocks within the central portion of the 
Santa Monica Mountains consist of Late Jurassic (?) 
slates of the Santa Monica Formation (Hoots 1931) . 
To the east, including large portions of the Verdugo 
Mountains, the basement rocks consist of intrusive 
plutonic rocks of quartz dioritic or granodioritic 
composition similar to rocks of Late Cretaceous age 
found in the San Gabriel Mountains (Lamar 1961) . 

The San Gabriel Mountains south of the San Ga- 



102 San Fernando Earthquake of 1971 



briel fault contain basement i o< k s that include 
schists, and quartzites, which are associated with and 
intruded by quartz diorite (Oakeshotl 1958). These 

r(x:ks arc all intruded by Upper Jurassic to Lowei 
Cretaceous granitics. North oi the fault, the base- 
ment rocks contain Meso/oic syenite, hornblende 
diorite, and Precambrian gneiss and gabbros that are 
also intruded by Upper Jurassic to bower Cretaceous 
granitic rocks. 

Upper Cretaceous (Chico Formation). — The oldest 
sedimentary rocks of the San Fernando Valley area 
(Chico Formation) are exposed at the surface in the 
Simi Hills. They consist of massive marine sandstones 
and coarse conglomerates, interbedded with shale. 

Eocene (Martinez and Domengine Formations). — 
The Eocene is represented by the Martinez and Do- 
mengine Formations (California State Water Rights 
Board 1902) . The Martinez, older of the two forma- 
tions, is exposed along the San Gabriel Fault and 
consists of a series of coarse marine shales, sand- 
stones, and conglomerates. The Domengine Forma- 
tion is composed of massive marine standstones and 
conglomerates that are exposed along the northwest- 
ern margin of the valley. 

Miocene (Topanga and Modelo Formations). — The 
Topanga Formation makes up the lower to middle 
portion of the Miocene and is composed of coarse 
marine and continental sandstone and conglomerate 
beds, interbedded with andesite and basalt flows. 
The upper Miocene is made up of a series of marine 
conglomerate and fine-to-coarse-grained sandstones, 
interbedded with diatomaceous shales (Modelo For- 
mation) . The Modelo may underlie the whole valley 
(California State Water Rights Board 1902) . 

Pliocene (Repetto and Pico Formations). — The 
lower portion of the Pliocene is composed of the Re- 
petto (Towsley) Formation, which consists of ma- 
rine siltstones and mudstones combined with lesser 
amounts of sandstone and conglomerate. The middle 
and upper Pliocene Pico Formation is mainly com- 
posed of marine siltstones, sandstones, and conglom 
erates, which grade into younger nonmarine sand- 
stone, mudstone, and conglomerate. Both formations 
may be included under one name, Fernando, as 
suggested by Lamar (1970) . 

Pleistocene (Saugus and Pacoima Formations). — 
The lower Pleistocene Saugus Formation consists of 



well-graded and poorly conyjlidated conglomerate 
and coarse-grained sandstone he-els (Oakeshotl 1' 
1 he- formation is mainly of continental origin, hut 

may grade into older and generally fme-r marine 
merits. 

The Pacoima Formation ('middle Plei 
consists ol well-graded reddish-brown fanglorm 
and conglomerate l>m^ on Saugus Formation gTavels 
and underneath terrace deposits around the- southern 
margin ol the San Gabriel Mountains. 

Upper Pleistocene tej Recent "ejlder alluvium" 
consists ej uplifted, poorly c onsejlidated, unsorted, 
angular-to-subangulai fanylomerate and terrace gTav- 
els. 

Recent. -The alluvial materials of the San Fernando 
Valley vary frcrm lexation tej location, dependir 
the- soiihc- leKk. In the- western and extreme south- 
ern portions of the valley ('generally south of the Los 
Angeles River) , the alluvial materials c onsist of clay, 
silt, and sand-size particles derived from sedimentary 
rocks which make up large portions of the Simi Hills 
and the Santa Susana and Santa Monica Mountains 
(fig. 1). In the northernmost portion of the valley 
(Sylmar-San Fernando area) and the east valley area 
south to the Uos Angeles River, the deposits are 
much coarser: they range from boulder size near 
the San Gabriel Mountains to sand, silt, and gravels 
near the Los Angeles River (California State Water 
Rights Board 1902). 

STRATIGRAPHY OF LOS ANGELES BASIN 

Basement Rocks. — The basement rocks of the Los 
Angeles Basin have been divided into two groups by 
Yerkes et al. (1905) on the basis of lithology. The 
groups, known as the "eastern" and "western" com 
plexes, are separated by the Newport-Inglewood and 
Santa Monica fault zones. 

The western complex (west of the Newport- 
Inglewood fault) , composed of Catalina schist, i; 
exposed in the Los Angeles Basin (cross sectior 
A-A') only in the Palos Verdes Hills. This comple> 
consists of fine-grained chlorite-quartz schist anc 
blue glaucophane-bearing schist of unknown, unde 
termined, or not definitely known age or strati 
graphic position (Woodring et al. 1940) . 

The basement rocks of the eastern complex ar> 
composed of Late Cretaceous granitic intrusive* 



Triassic metasedimentary schists, and a series of vol- 
canics of probable Late Jurassic age (cross section 
C-C') . 

Paleocene, Eocene, and Oligocene. — Rocks of Paleo- 
cene, Eocene, and Oligocene age do exist in the Los 
Angeles Basin (Vaqueros, Sespe, Santiago, and Sil- 
verado Formations) , but are not considered in this 
report because they are not included in the cross sec- 
tions or site model studies. 

Miocene (Topanga, Modelo, Monterey, and Puente 
Formations). — Rocks of the Los Angeles Basin area 
of middle to lower Miocene are, for the most part, 
included in the Topanga Formation which consists 
of marine well-bedded sandstones, siltstones, and 
massive conglomerates. Late Miocene rocks are in- 
cluded in the equivalent, or nearly equivalent, Mo- 
delo, Monterey, and Puente Formations. Lithologi- 
cally, these formations include marine shales of 
various types, sandstone, conglomerate, and, in the 
Palos Verdes Hills (Monterey Formation) , mud- 
stone, diatomaceous shale, and interbedded siltstone, 
sandstone, limestone, and conglomerate beds 
(Woodring et al. 1946) . 

Pliocene (Repetto and Pico Formations). — Rocks of 
Pliocene age have been divided into two formations 
— Repetto (lower Pliocene) and Pico (upper Pli- 
ocene) — by many authors. Recently, Lamar (1970) 
has combined the two formations and used the name 
Fernando Formation, as was mentioned earlier in 
the section on the Stratigraphy of San Fernando Val- 
ley Area. The name Fernando was first used by Eld- 
ridge and Arnold in 1907. Lamar's Fernando Forma- 
tion includes "rocks lying between the Puente 
Formation and the younger alluvial and terrace de- 
posits," and consists of marine tan-to-brown siltstone, 
sandstone, shale, and conglomerate beds. 

Pleistocene (San Pedro Formation and Terrace De- 
posits). — Lower Pleistocene rocks (San Pedro For- 
mation) include marine silt, sand, and gravels and 
are overlain, at various localities, by upper Pleisto- 
cene marine and nonmarine terrace deposits. These 
terrace deposits include, respectively, marine and 
nonmarine sand, gravel, and silt. 

Recent. — Recent deposits include dune sand (south 
of Ballona Creek and near the present-day coastline) 
and alluvial materials that consist of sand, gravel, 
and silt in the stream channels and beneath the flood 
plains (Poland et al. 1959). 



Subsurface Geology of Earthquake Area 163 

REFERENCES 

Bailey, T., and Jahns, R., "Geology of the Transverse Range 
Province," California Division of Mines Bulletin 170, Ch. II, 
No. 6, Sept. 1954, pp. 83-106. 

California State Water Rights Board, "City of Los Angeles vs. 
City of San Fernando, et al.," San Fernando Valley Refer- 
ence Report of Referee No. 650079, Vols. I and II, Superior 
Court, Los Angeles County, Calif., July 1962. 

Corbat6, Charles E., "Bouguer Gravity Anomalies of the San 
Fernando Valley, California," California University Publica- 
tions in Geological Sciences, Vol. 46, No. 1, University of 
California Press, Berkeley, Nov. 1963, pp. 1-32. 

Eldridge, G.H., and Arnold, Ralph, "The Santa Clara Valley, 
Puente Hills, and the Los Angeles Oil Districts, Southern 
California," Geological Survey Bulletin 309, U.S. Department 
of the Interior, Washington, D.C., 1907, 266 pp. 

Hoots, Harold W., "Geology of the Eastern Part of the Santa 
Monica Mountains, Los Angeles County, California," Geo- 
logical Survey Professional Paper 165-C, U.S. Department of 
the Interior, Washington, D.C., 1931, 134 pp. 

Jennings, C.W., Geologic Map of California, Long Beach 
Sheet. California Division of Mines and Geology, Sacra- 
mento, 1962, scale 1:250,000. 

Jennings, C.W., and Strand, R.G., Geologic Map of Cali- 
fornia, Los Angeles Sheet, California Division of Mines and 
Geology, Sacramento, 1969, scale 1:250,000. 

Lamar, Donald L., "Structural Evolution of the Northern Mar- 
gin of the Los Angeles Basin," Ph. D. thesis, University of 
California, Los Angeles, 1961, 142 pp. 

Lamar, Donald L., "Geology of the Elysian Park-Repetto Hills 
Area, Los Angeles County, California," California Division 
of Mines and Geology Special Report 101, Sacramento, 1970, 
45 pp. 

Merifield, P.M., "Geology of a Portion of the Southwestern 
San Gabriel Mountains, San Fernando and Oat Mountain 
Quadrangles, Los Angeles County, California," M. A. thesis, 
University of California, Los Angeles, 1958, 61 pp. 

Oakeshott, Gordon B., "Geology and Mineral Deposits of San 
Fernando Quadrangle, Los Angeles County, California," 
California Division of Mines Bulletin 172, Feb. 1958, 147 pp. 

Poland, Joseph F., Garrett, A. A., and Sinnott, Allen, "Geology, 
Hydrology and Chemical Character of Ground Waters in 
the Torrance-Santa Monica Area, California," Geological 
Survey Water-Supply Paper 1461, U.S. Department of the 
Interior, Washington, D.C., 1959, 425 pp. 

Proctor, R.J., "La Crescenta Tunnel Route," Metropolitan 
Water District of Southern California, Los Angeles, June 

1964, scale 1:12,000 (unpublished geologic map and section) . 
Proctor, R.J., "Flint Ridge Tunnel Route," Metropolitan 

Water District of Southern California, Los Angeles, May 

1965, scale 1:12,000 (unpublished geologic map and section) . 
Proctor, R.J., "Sepulveda Tunnel Route," Metropolitan Water 

District of Southern California, Los Angeles, June 1967, 
scale 1:12,000 (unpublished geologic map and section) . 

Proctor, R.J., "Verdugo Tunnel Route," Metropolitan Water 
District of Southern California, Los Angeles, Nov. 1970, 
scale 1:12,000 (unpublished geologic map and section). 

Rogers, T.H., Geologic Map of California, Santa Ana Sheet, 



104 



San Fernando Earthquake of 1971 



California Division of Mines and Geology, Sacramento, 1965, 
scale 1:250,000. 

Rogers, T.H., Geologic Map of California, Sun Bernardino 
Sheet, California Division ol Mines and Geology S.kih 
mento, 1967, scale 1:250,000. 

Schoellhamer, J.E., and Woodford, A.O., "The Flooi ol the 
Los Angeles Basin, Los Angeles, Orange and s.m Bernai 
dino Counties, California," Geological Survey Oil and (.as 
Division Map OM-117, U.S. Department oi the Interior, 
Washington, D.C, 1951, scale 1:500,000. 

U.S. Geological Survey and the National Oceanic and Atmos- 
pheric Administration (Publishers), the Sun Fernando, Cali- 
fornia, Earthquake of February 9, 1971, Geological Si 
Professional Paper 733, U.S. Department of the Interior and 
U.S. Department of Commerce, Washington, D.C, 1971, 
254 pp. 

Woodring, W.P., Bramlette, M.N., and Kew, W.S.W., "Geo! 
ogy and Paleontology of the Palos Verdes Hills, California," 
Geological Survey Professional Paper 207, U.S. Department 
of the Interior, Washington, D.C. 1946, 1 15 pp. 

Ycrkes, R.F., McCulloh, T.H., Schoellhamer, J.E., and Ved- 
der, J.G., "Geology of the Los Angeles Basin. California 
— An Introduction," Geological Survey Professional Papei 
420-A, U.S. Department of the Interior, Washington, D.C, 
1965, 57 pp. 



BIBLIOGRAPHY 

Used to construct general geologic map and cross sec- 
tions 

Barrows, A.G., Kahle, J.E., Weber. F.H., Jr., and Saul, R.B., 
Map of Surface Breaks Resulting From the San Fernando, 
California, Earthquake of February 9, 1911 , Preliminary Re- 
port II, Plate I, California Division of Mines and Geology, 
Sacramento, 1971, scale 1:24,000. 

California Department of Water Resources, "Planned Utiliza- 
tion of the Ground Water Basins of the Coastal Plain of 
Los Angeles County, Appendix A, Ground Water Geology," 
Bulletin 104, Sacramento, 1961, 181 pp. 

California Department of Water Resources, "Crustal Strain and 
Fault Movement Investigation, Faults and Earthquake Epi- 
centers in California," Bulletin 116-2, Sacramento, Mar. 5, 
1964, 96 pp. 

California State Division of Oil and Gas, California Oil and 
Gas Fields Supplemental Maps and Data Sheets, Dept. of 
Conservation, Sacramento, Sept. 1969, 183 pp. 

Cordova, Simon, "El Segundo Oil Field," Summary of Opera- 
tions, California Oil Fields, Vol. 49, No. 2, State of Cali- 
fornia Division of Oil and Gas, Sacramento, 1963, pp. 45-52. 

Crowder, R.E., "Los Angeles City Oil Field," Summary of 
Operations, California Oil Fields, Vol. 47, No. 1, State of 
California Division of Oil and Gas, Sacramento, Jan.-June 
1961, pp. 67-78. 

Crowder, R.E., "Cheviot Hills Oil Field," Summary of Opera- 
tions, California Oil Fields, Vol. 54, No. 1, State of Cali- 
fornia Division of Oil and Gas, Sacramento, 1968, pp. 17-21. 



Dosch, M.W.. and I '■'■ I Band Sum, 

nun, of Operation Californ Field 
St. iir ol California Division ol Oil and '■ 
J.,., fun* 1958, pp r > Yl 

Dulu C Martin, and I - id J. "Sii I 

Southern California Strong-Motion Earthquake Stat 
1 ', of California, l.os Angeles Report (,: 

pp. and an appendix. 

Durrell, C, "Geology of the Santa Monica Mountains Is* 
Vngeles and Ventura Counties, Map SI - ( alifornU 

Division of Mines Bulletin 170, Sept. 1954, stale l:12< 

Ktkis. Rollin, "Geology and Ground Water Si 
of Valley Fill," California Division of Watei Bul- 

letin 15, Department of Watei Resources Sacramento, 1954, 
279 pp. 

Holmes, L.C., Soil Survey of the San Fernando Vallej Area, 
California. U.S. Department of Agriculture. Washington, 
I)( [916 63 pp. 

Jenkins, O.P. (Editor), "Geologic Formations and Economic 
Development of the Oil and Gas Fields of California," 
California Division of Mines Bulletin 118, San Francisco, 
Apr. 19)3. 773 pp. 

Jennings, C, and Hart. F., "Exploratory Wells Drilled Outside 
of Oil and Gas Fields in California to December 1953," 
California Division of Mines Special Report 45, San Fran- 
cisco. 1956. 101 pp. 

Johnson. R. V. "Boyle Heights Oil Field." Summary of Opera- 
tions, California Oil Fields. Vol. 52, No. 1. State of Cali- 
fornia Division of Oil and Gas, Sacramento, 1966. pp. 69-72. 

Lastrico, R.M.. "Effects of Site and Propagation Path on Re- 
corded Strong Earthcpjake Motions." Ph. D. thesis. School of 
Engineering and Applied Science. University of California, 
l.os Angeles. 1970. 205 pp. 

Los Angeles County Flood Control District. Coastal Plain 
Ground-Water Contours Shallow Aquifers Map, Los Angeles, 
Calif., Apr. 1969c7, scale 1:63,360. 

Los Angeles Countv Flood Control District, San Fernandc 
Valley Ground-Water Contour Map, Los Angeles, Calif. 
Apr. 19696, scale 1:63.360. 

McCulloh, T.H.. "Gravity Variations and the Geology of the 
Los Angeles Basin of California." Geological Survey Profes 
sional Paper 400-B. U.S. Department of the Interior, Wash 
ington, D.C. 1960. pp. 320-325. 

Merifield. P.M., "Geologv of a Portion of the Southwesterr 
San Gabriel Mountains. San Fernando and Oat Mountaii 
Quadrangles. Los Angeles County, California." M.A. thesis 
University of California. Los Angeles. 1958. 61 pp. 

Smith. M.. Geological Survey Oil and Gas Investigation Map 
ON-2I5. Sheet 2. U.S. Department of the Interior, Wash 
ington, DC, 1969, scale 1:500.000. 

Winterer, E.L., and Durham. D.L.. "Geology of Southeaster! 
Ventura Basin. Los Angeles Countv, California." Geologica 
Survey Professional Paper 334-H. U.S. Department of th 
Interior, Washington. D.C. 1962. 366 pp. 

Woodford, A.O., Schoellhamer, J.E., Vedder, J.G., and Verke 
R.F., "Geology of the Los Angeles Basin," California Dn 
sion of Mines Bulletin 170, Ch. II, No. 5. Sept. 1954, pj 
65-81. 



Subsurface Investigation of 

Ground Rupturing 

During San Fernando Earthquake 



CONTENTS 

Page 

Introduction 

Tujunca Segment of San Fernando 

Fault 
Sylmar Segment of San Fernando 

Fault 
Conclusions 



165 
165 

166 



171 



EDWARD G. HEATH 
F. BEACH LEIGHTON 

F. Beach Leighton & Associates 
Engineering Geologists 
La Habra, Calif. 



INTRODUCTION 

Alter the San Fernando earthquake of February 9, 
1971, geologic mapping of the numerous cracks, 
scarps, and other evidence of ground rupturing that 
occurred throughout the Sylmar-San Fernando area 
was begun. Reconnaissance mapping showed that 
most ground ruptures were concentrated along two 
main tectonic alignments now referred to as the Syl- 
mar and Tujunga segments of the San Fernando 
fault. Because neither of these fault segments had 
been mapped by geologists before the February 9 
event, two questions immediately arose: "Could 
these faults have been discovered and mapped before 
the earthquake?" and "What kind of data would be 
required to determine if preexisting and potentially 
active faults did exist in these locations?" 

To help answer these questions, a subsurface geo- 
logic investigation utilizing largely backhoe trenches 
was organized in cooperation with the California Di- 
vision of Mines and Geology (CDMG) . Fourteen 
trenches were excavated to depths ranging from 6 to 
14 feet and were logged generally at a scale of 1:60. 
Selection of trench locations was determined by: (1) 
patterns of recent ground breakage; (2) known rela- 
tion of overburden, alluvium, and alluvium in con- 
tact with bedrock; and (3) accessibility and authori- 
zation to excavate. 



TUJUNGA SEGMENT OF SAN FERNANDO 
FAULT 

Seven of the 14 trenches were excavated along the 
Tujunga segment and related faults farther to the 
north. Logs 1, 2, 3, 6, and 8 are included herein be- 
cause they are most significant. 



165 



166 San Fernando Earthquake of 1971 



Trenches I and 2 were excavated in Lopez Can 
yon across a recent fault branch located approxi- 
mately y 2 mile north of the main trace ol the fault 
segment near the canyon mouth ('fig. I). The fault 
is parallel, and apparently related, to the 1 ujunga 
fault segment. Trench 1 (fig. 2) was located where 
the faulting produced a nearly vet tied '.-foot-high 
scarp. Examination of the test trench showed that re- 
cent alluvial sands had been offset approximately 32 
inches by one fault trace and that these alluvial 
sands rest on different bedrock on both sides of the 
fault. A second fault, showing offset of the bedrock 
and bedrock in fault contact with alluvial sands, is 
also exposed in the test trench. Therefore, this trench 
exposed evidence that the faulting of February 9, 
1971, occurred along previously existing faults which 
could have been detected by trenching before t he- 
February 9 event. 

Trench 2 (fig. 3) was located 85 feet east of 
Trench 1, along the same fault trend where the fault 
is expressed at the surface by a 3-foot-high flexure 
approximately 60 feet in width. No ground breakage 
was observed at the surface in the immediate area of 
the test trench. The trench itself revealed approxi- 
mately 3 feet of very recent stream deposits overlying 
3 to 4 feet of old fill which, in turn, overlies recent 
sands and gravels. There was no indication of tec- 
tonic disturbance of any of these units other than 
the same gentle warp that was evident at the surface. 
Trench depth was limited to approximately 8 feet by 
caving of the loose sand and gravel near the bottom. 
Comparison of Trenches 1 and 2 reveals the extreme 
variation that can occur along the strike of a fault in 
a distance of only 85 feet. It also illustrates the need 
for more than one test trench along a particular fea- 
ture to define accurately the nature of the geologic 
conditions. 

Trench 3 (fig. 4) was located approximately 3,000 
feet east of the mouth of Lopez Canyon across a 3- to 
6-inch surface scarp of the Tujunga fault segment. 
At this location, an 8-foot-deep test trench revealed a 
section of Modelo siltstone and shale that had been 
thrust at an angle of approximately 45° over a Qua- 
ternary fanglomerate. Approximately 12 feet of re- 
verse dip-slip movement could be seen in the trench. 
This movement far exceeds the 3 to 6 inches of 
movement caused by the February 9 event, indicat- 
ing that this fault has been active in recent time. 
Therefore, this trench clearly revealed the prior ex- 



istence ol a Quaternary or youngei fault at tins le> 
cation, and the- fault could I en classified as 

potentially active had a trench been excavated and 
properly logged before the February 9, 1971, event 

Trench 6 (fig- 5) was excavated where the- Tu- 

junga lault segment crosses Kig Tujunga Wash. At 
this location, the- fault scarp ranged from 1 \/, {< 
feet high. J Ik- excavation exposed loose alluvial sand 
and gravel thai limited the trench depth to 7 to 8 
feet because- ol side-wall sloughing. The lault /one 
in the- eejarse sediment was a jumbled /out that cut ij 
across the- stratified units. J here was, however, no in- 
dication e,f prior earth movement in the area; it is, 
there-hire-, presumed that the faulting observed in the 
trench was entirely caused by the February 9 move- 
ment. This trench, however, does illustrate that care- 
ful and detailed trench examination can reveal fault- 
ing in loose and unconsolidated sand and gravel 
deposits. 

Trench 8 (fig. 6) was excavated across the Tu- 
junga segment at the mouth of Lopez Canyon. The 
trench was entirely in the upper Miocene Modelo 
siltstones and sandstones. Near the fault zone, these 
units were highly sheared and contorted, giving evi- 
dence of substantial prior faulting and ground move- 
ment. Because of the exceptional folding and fault- 
ing in this trench, the trench was mapped at the 
scale of 1:12 by CDMG personnel. Holocene sedi- 
ments were not exposed in the trench; therefore, the 
most recent age of faulting before February 9, 1971, 
could not be determined at this location. 

SYLMAR SEGMENT OF SAN FERNANDO 
FAULT 

Three test trenches (logs 5, 12, and 13) were exca- 
vated across the eastern end of the Sylmar segment 
and are included here because they represent the 
variations in usable data that can be obtained from 
test trenches and also illustrate some typical trench- 
ing problems. 

Trench 5 (fig. 7) was located adjacent to Newton 
Street where the Sylmar fault segment crosses Pa- 
coima Wash. The excavation cut across a 1 -foot-high 
fault scarp produced by the February 9 event and ex- 
posed an extremely coarse boulder gravel of recent 
alluvial sediments of the wash. The ground rupture 
could be traced no more than 1 foot below the sur- 
face into these coarse materials. Severe sloughing of 



Subsurface Investigation of Ground Rupturing 167 




S 

bo 



e 

S" 

s 



C 
O 



E 



3 
ho 



IfiH 



San Fernando Earthquake of 1971 



Logged by Heath Northern Trace - Lopez Canyon 

I'n la 

I vi" "i i ir '■•■ i i«i. i 


ATTITUDES 


. , . , 






ID Beddlni 
N77W, 71N 

© Bedding plana raull 

NMOW, 75N 

r.'ii Fault 

N75W, (J2N 


QaJ ft Swi Alluvium and slopi 

pebbli Veil bedd 1 -, etraejD deposit* villi eomi i* bblee and 

Sit, Si II mi 

0a ' sit, Bend added, bedeupto4 < U 

Cg > Ss, Conglomerate and aandatooe matrix white, clean, ig. ami m, t... ■ Ijm ap 


bud 

i bard 




NAT i hAI. 
■ LI 


Hon* 



(,HA I'll If 1(1. I'M I SI M AT ION 







Figure 2. — Geologic pit log for Trench 1. 



;raphic representation 



Logged by Heath 
Tvoe of rie backhoe 




B6 E of trench 1, Northern Trace Lopez Canyon 
Pit location 




T ract Lopez Canyon 
Date 4-12-71 


ATTITUDES 


ENGINEERING GEOLOGY DESCRIPTION 


PHYSICAL 
CONDITION 


COMMENTS 


None 


Qal, 

Fill, 
Soil, 
Qalo, 


Alluvium, light gray sand and some gravel, deposited on fill, as late as 
spring floods of 1969, crudely bedded. 

Dark gray brown, mass to poorly laminated, sandy 

Dark brown-black, carbonaceous, buried grass and roots. 

Light gray, older alluvium, gravel and boulders in sand. 


Soft and friable 
Soft 

Soft 

Soft-firm 


No f- - 
in trench 
36"-42" uplift 
on north side 
by warping only 


NAT URAL 
SLOPE 


Graded flat 



trend= N3E 




Figure 3. — Geologic pit log for Trench 2. 



Subsurface Investigation of Ground Rupturing 169 



Logged by Heath Ridge north of Carl Street east of Van Nuys Boulevard Dat« 4-12-71 

Pit location 


ATTITUDES 


ENGINEERING GEOLOGY DESCRIPTION 


PHYSICAL 
CONDITION 


COMMENTS 


©Fault E-W, 44N 
apparent dip 37 

(g)Bedding N85E, 44N 

©Bedding N80E, 55N 

©Bedding N81E, 28N 


Cg, Conglomerate, light yellow brown, pebbles to cobbles in coarse sand matrix, 
angular to well rounded clasts, some caliche along joints and root tubes, 
locally silty, minor clay content, possibly alluvial fanglomerate. 

Sit + Sh, Siltstone and shale, buff to rust brown, thinly bedded alternately cemented beds, 
highly fractured some dragfolds and contorted bedding. 


Firm-hard 

No open fracturing 

Soft, firm to hard 


Well defined 
single fault 
plane 


NATURAL 

SLOPE 





GRAPHIC REPRESENTATION 



Pit trend= N6E 




Figure 4. — Geologic pit log for Trench 3. 



GRAPHIC REPRESENTATION 



Looted by Dickey Big Tujunga Wash, North Side Tract Big Tujunga 
Type of rig 24" backhoe Pit locatUm Da te 4-15-71 


ATTITUDES 


ENGINEERING GEOLOGY DESCRIPTION 


PHYSICAL 
CONDITION 


COMMENTS 


Flat lying bedding 


Sand soil. Fine to coarse sand with roots and plants 
Bldrs, Boulders with sand and pebbles 
Pbls + Sd, Pebbles and medium to coarse sand 
Sd, Fine micaceous sand, £" to 2" thick bed 
Bldrs + Cbls, Boulders and cobbles with sand matrix 

Note: Fault zone marked by boulders on end, generally not flat lying, as above. 


Loose 
Loose 
Loose 

Damp, loose 
Loose 


Difficult to 
conclude active 
fault without 
surface offset. 
Correlation is 
tentative. 


NATURAL 
SLOPE 


Flat lying 
Surface offset 
of 16-22" 




Figure 5. — Geologic pit log for Trench 6. 



170 San Fernando Earthquake of 1971 



Logged b) . 

Noti 0) Dickey 

l .i I » IIIWII) 






ATTITUDES 



• u N i 

n, i6N 

"I < 
i "iv, 33N 



OLOi 



Shi 'i Bit, 



i 






Conl i 









C t, M I 







Figure 6— Geologic pit log for Trench 8. 



GRAPHIC REPRESENTATION 



Logged by Heath Newton Street and Svlmar Fault Segment Tract Newton Street 
Type of rig backhoe plt locatlon Date 4-13-71 


ATTITUDES 


ENGINEERING GEOLOGY DESCRIPTION 


PHYSICAL 
CONDITION 


COMMENTS 




Qal, alluvial gravels, cobbles and boulders up to 2' across, average 2"-6" in very 
coarse sand matrix. Sand 30+ %, pebbles, cobbles and boulders 70 
Some crude bedding where sandy. 

Note: Trench caved badly, could not expose face over 4' high. 


Loose 

Caves easily 


Fault line could 
not be traced 
in gr^ 

Trench caved 
badly. 


NATURAL 
SLOPE 


1 



Pit trend= N42E 




Figure 7. — Geologic pit log for Trench 5. 



Subsurface Investigation of Ground Rupturing 171 



the trench walls limited the depth of the trench to 
approximately 6 feet and prevented the exposure of 
a sufficient section of coarse sediments so as to be di- 
agnostic. This trench emphasizes that, even with a 
known fault that has at least 1 foot of displacement, 
coarse unconsolidated gravel having boulders up to 2 
feet across and averaging 2 to 6 inches can defy fault 
definition. 

Trench 12 (fig. 8) was excavated approximately 
1,000 feet west of Trench 5 across a gentle topo- 
graphic warp. There was no evidence of actual 
ground breakage at the trenching site, though ground 
rupturing had occurred through residences on both 
sides of the site. The excavation exposed terrace 
sands and gravels that conformed to the surface 
warping and, though slight fracturing was observed, 
offset of bedding surface was not evident. The only 
indication of deeper breaks was the relatively narrow 
(approximately 50 ft wide) zone of warping. 

Trench 13 (fig. 9) was excavated next to the Foot- 
hill Freeway at a location approximately 1,000 feet 
west of Trench 12. Here, the north side of the free- 
way shows a 3- to 4-inch vertical scarp, with 7 to 8 
inches of left-lateral movement. The test trench was 
in terrace sand and gravel, and the fault trace could 
readily be followed in the trench. The total offset of 
the bedding could not be established, but it was 



greater than the 3 to 4 inches of vertical movement 
observable at the surface. It can be concluded that 
faulting had taken place at this location before the 
February 9 event. 

CONCLUSIONS 

Trenching along the Tujunga segment revealed 
the following tectonic events: (1) preexisting bed- 
rock faulting that had contorted and sheared units 
of the Modelo Formation of late Miocene age; (2) 
thrusting of Modelo units over Quaternary fanglom- 
erate; (3) alluvium in preearthquake fault contact 
with the Repetto Formation; and (4) displacement 
of both Holocene alluvial sediments and bedrock 
during the February 9 earthquake. Trenching along 
the Sylmar segment clearly shows that Quaternary 
terrace deposits had been offset by faulting before 
the February 9 event. 

The subsurface trenching program demonstrated 
that faults readily can be observed and mapped in 
test trenches, 6 to 15 feet deep, whether these are 
dug in youthful alluvial sands, Quaternary fanglom- 
erates, terrace deposits, or bedrock units. However, 
commonly two or three trenches must be located 
along a suspected fault zone to establish with cer- 
tainty the presence or absence of faulting. 



GRAPHIC REPRESENTATION 



Logged by Heath Adjacent to 12670 Gladstone 

Type of rig backhoe Pit location Date 6-30-71 


A T T I T I' D E S 


ENGINEERING GEOLOGY DESCRIPTION 


PHYSICAL 

CONDITION 


COM M EN r S 


None 


Old fill. Gravel, soil and debris 

Cg, Conglomerate, alluvial, Light- medium brown, subangular to well rounded pebbles, 
cobbles, and boulders up to 2\ average 3"-6", sandy malnx 

Sd , Sand, medium-dark brown, fine-medium sand, silty and clayey with common 
pebbles up to ^" 


Loose, uncon- 
solidated, 
slightly damp 

Loose, friable 
damp 


Trench shows 
nu significant 
breaks, bedded 
strata bend to 
conform to 
surface warp 
or scarp 


NAT I RA L 
SLOPE 







Pit trend= N5E 




Figure 8. — Geologic pit log for Trench 12. 



172 San Fernando Earthquake of 1971 

Detection of faulting in tesi trenches excavated in optimum trenching condition! hk- those in whu 

loose, coarse alluvium is difficult, l>ui detailed map ceni alluvial and oldei alluvial sediments are in con 

ping ran help 10 identify jumbled fault /ones. J Ik- tacl with bedrock units. 



GRAPHIC I' 



i ogged b , Dickey 


Maclay Mn-i 1 




I n*..l !/. 


1 bj i/ickoy 

1 vi..- ol riK 2\" backhoc 




a i m in a 


ENG1 




1 


None 


I'cii. dep, Silty sand iitH 

Siiv bldra Bould 

d, , 

Bldrs, Bould rs wit] 


damp 
lamp 


. 


SI.' 









Figure 9. — Geologic pit log for Trench 13. 



Trench Exposures Across 

Surface Fault Ruptures 

Associated With San Fernando Earthquake 



CONTENTS 

Page 

173 Introduction 

173 Bartholomaus Ranch Trenches 

174 Surface Evidence of Faulting 

175 Subsurface Evidence of Faulting, 

Trench A 

176 Evidence of Faulting Prior to 1971, 

Trench A 
111 Subsurface Evidence of Faulting, 

Trench B 
178 Evidence of Faulting Prior to 1971, 

Trench B 
178 Brown Trench 

178 Surface Evidence of Faulting 

179 Subsurface Evidence of Faulting 
179 Evidence of Faulting Prior to 1971 

179 Oak Hill Trench 

181 Discussion and Conclusions 

182 References 

Publication authorized by Director, 
U.S. Geological Survey. 



M. G. BONILLA 

U.S. Geological Survey 
Menlo Park, Calif. 



INTRODUCTION 

This report gives the principal results of the exam- 
ination of several exploratory trenches excavated 
across the February 9, 1971, surface fault ruptures. 
The trenches, some dug for the U.S. Geological Sur- 
vey and some for other organizations, were exposed 
at various times from April through August 1971. 
Results of detailed study of four trenches are pre- 
sented, followed by generalizations based on investi- 
gation of those trenches, seven trenches examined in 
reconnaissance, and trench data reported by others. 

Special thanks are due C. T. Brown, Ellen Dubois, 
and W. D. Bartholomaus for permission to trench on 
their property; G. J. Lensen of the New Zealand 
Geological Survey, and J. B. Pinkerton, J. Schlocker, 
and J. N. Alt of the U.S. Geological Survey for col- 
laboration in the mapping of various trenches; the 
California Division of Mines and Geology and F. 
Beach Leigh ton 8c Associates for inviting the author 
to examine their trenches; and the U.S. Atomic En- 
ergy Commission, Division of Reactor Development 
and Technology, for partial support of the work. 

BARTHOLOMAUS RANCH TRENCHES 

Two trenches were excavated across the February 
9 surface ruptures about 0.3 km north of the Pacoima 
Memorial Lutheran Hospital on the Bartholomaus 
Ranch (Trenches 3, 4, fig. 1) . Each trench was 0.9 m 
wide and 3.7 m deep. The western trench (A, fig. 2) 
was 46 m long and the eastern trench (B, fig. 2) was 
38 m long. Trench A was located in alluvial deposits 
at the mouth of a small canyon with the expectation 
that bedded sediments would be found; Trench B 
was located so as to expose the contact between the 
bedrock (Modelo Formation) composing the hills 



173 



171 San Fernando Earthquake <>\ 1971 




Figure 1. — Index map showing location of trenches and generalized trace of surface faulting. Number* idrntif-) trenches: 1, By own Trench; 
2, Oak Hill Trench; }, Bartholomaus Ranch Trench A, -), Barlholomaus Ranch Trench II. Fault trace* modified from i S Cmlogical 
Survey Staff (1971, fig. 2). 




-. ■!■■' ' m ! ■ » ■— ; i TT gTT_ >: T* 



Figure 2. — Vertical aerial photograph (taken Feb. 12, 1971) of part 
of Bartholomaus Ranch, showing surface ruptures and locatioyis 
of trenches A and B. 



and the surficial deposits at the base of the hills. 
Details of the surface ruptures were destroyed by 
cultivation before the trench sites were selected, but 
aerial photographs taken February 12 were used to 
insure that the trenches crossed the ruptures. 



Surface Evidence of Faulting 

The faulting in this area was expressed at the sur- 
face by a series of small furrowlike ruptures of the 
soil in a zone some 30 m wide, accompanied by var- 
ious differences in elevation across the zone. The 
ruptures appear in figure 2 as a series of subparallel, 
irregular white lines and light-colored zones. A dif- 
ference in elevation across the zone, north side up, 
was visible on aerial photographs and on the ground 
along most of the rupture zone. A view of the rup- 
ture zone, where it crossed the road west of Trench 
A, is shown in figure 3. The vertical component of 
displacement was about 30 cm on the rupture in the 
foreground and about 80 cm across the whole zone. 
Trench A was about 10 m east of the road where the 
prominent rupture shown in figure 3 had split into 
two branches and where the vertical component 
across it was less than at the road. Cultivation of the 
surface prevented direct measurement of the fault 
displacement, and the ground surface profile (fig. 4) 
does not show any clear-cut scarp. The ground sur- 
face profile of Trench B (fig. 6) indicates that the 
vertical component of displacement there was about 
60 cm and that most of this displacement occurred 






Trench Exposures Across Surface Fault Ruptures 175 










Figure 3. — View northward across zone of surface ruptures from a 
point near south end of Bartholomaus Ranch Trench A. Marks 
on stick are at 1-foot (OJ-m) intervals. Bottom of stick is on sur- 
face of road in foreground. R. F. Yerkes photograph (date Feb. 
10, 1971). 



in the northern one-third of the 19-m-wide zone of 
visible surface ruptures. 

Subsurface Evidence of Faulting, Trench A 

In Trench A, one definite fault and several proba- 
ble faults were found in the poorly bedded alluvial 
materials revealed in the trench. A description of the 
sediments is given below, followed by a description 
of the faults. 

The oldest sediment unit in the trench (A, fig. 
4) is friable-to-firm silty fine sand containing scat- 
tered angular pebbles; no bedding was visible. A soil 
profile had developed in this unit before its burial 
by the overlying unit. The upper 0.8 m of the bur- 
ied soil is olive gray, slightly organic (judging from 
its color), and noncalcareous; the lower 1.2 m is 



light olive gray and contains calcium carbonate in 
the form of white spots and coatings on the pebbles. 
Thus, the entire exposed thickness of unit A is in 
the soil profile. Neither clay coatings nor develop- 
ment of soil structure was observed. The upper sur- 
face of this unit was partially eroded before deposi- 
tion of the overlying unit, producing the gully 
shown near point E (fig. 4) and other irregularities 
in the surface. The next younger unit (B, fig. 4) is 
more varied in grain size and development of bed- 
ding than unit A. It consists of obscurely bedded 
silty sand containing scattered angular gravel and 
cobbles; short lenses of laminated sand and silt or of 
bedded silty gravel and sand; and imbedded mix- 
tures of silty sand, gravel, and cobbles. In the lower 
part, it locally contains irregular areas of olive-gray 
slightly organic soil, apparently reworked material 
from the buried soil below; some of these areas are 
shown above unit A (fig. 4) . The surface soil is 
sandy silt and silty sand, slightly organic, slightly cal- 
careous in the lower 5 cm or so, and 30 to 50 cm 
thick. A subdivision of unit B was mapped in the 
southern part of the trench (C, fig. 4) . Unit C could 
be traced by its slightly darker color (light olive 
gray, 5Y 5/2 in the Munsell system) than by the 
overlying material (yellowish gray, 5Y 7/2) . It ap- 
peared to be slightly organic and was somewhat cal- 
careous 30 to 45 cm below its top; it probably repre- 
sents a surface soil slightly older than the modern 
soil. The youngest material recognized in the trench 
is artificial fill (D, fig. 4) above two buried pipe- 
lines. 

The fault at E (fig. 4) was clearly expressed in 
well-bedded sand and fine gravel (fig. 5) , but ob- 
scure in imbedded mixtures of silty sand and gravel. 
The apparent dip was 37 °S., and the apparent re- 
verse displacement was 2.5 to 5 cm. Its lower end 



8- 



8" 



2- 




24 28 

METERS 



48 



Figure •/. — Geologic section of west wall of Bartholomaus Ranch Trench A, showing approximate locations of surface ruptures (short 
vertical lines such as H) and ruptures exposed in trench (E, F, G). Surx'eyed points on ground surface indicated by dots. Dashes 
indicate approximate position of top of unit C and of boundary of unit D. See text for further explanation. 



170 San Fernando Earthquake of 1971 



"*&* 










*- 









** *s 



Figure 5. — Fault (F, fig. 4) in well-bedded sediments in west wall "/ 
Bartholomews Ranch Trench I. Scale in centimeters. 

was concealed by the timber supports, but possible 
offset of the upper contact of unit A probably would 
not have been visible because the contai t is not 
sharp. The fault could not be traced larther north; 
it either terminated there or was invisible in the 
unbedded sediments. The fault was not found in the 
east wall of the trench, apparently because it did not 
intersect well-bedded sediments. 

A group of fractures, probably faults, found in the 
trench below the southern part of the zone of surface 
ruptures is represented by fine lines near F on figure 
4. The south-dipping fractures appeared as soft zones 
a few centimeters thick whose prominence could be 
enhanced by careful brushing with a paint brush. 
Open cracks about 1 mm wide were visible along 
them in a few places, but these are not unequivo- 
cally diagnostic of faulting, because irregular desicca- 
tion cracks of similar width also developed in the 
trench walls. The north-dipping fracture zone indi- 
cated directly above F on figure 4 was first called to 
my attention by J. L. Smith (FUGRO, Inc.) . This 
zone was more obscure than the south-dipping frac- 
tures, but also consisted of narrow soft zones accom- 
panied, in places, by very narrow open cracks. No 
offset beds or consistently rotated pebbles were found, 
and neither the amount nor sense of displacement on 
these fractures could be ascertained. 

The north-dipping fracture indicated at G (fig. 4) 
was first seen on enlargements of photos of the 
trench walls and later confirmed in the field. It ap- 
peared primarily as a discontinuous open crack, but 
at one point seemingly displaced a thin deposit of 



laminated silt aboul 4 cm in a n i Unfor- 

tunately, the silt deposit is ric-ithc-i uniform in thick- 
ness, in expression of upper and lower contacts, nor 
iii general appearance; therefore a lum statement 
cannot be made about its former continuity. Smii- 
larly, where the fracture intersects unit C, the unit 
boundary especially south of the fracture is not 
sufficiently sharp to permit a firm conclusion as to 
whether ot not the boundary is offset. A difference 
in altitude and inclination of this boundary near the 
fracture is. however, visible in figure 1 and is dis- 
c ussed in a following paragraph. 

The fault and probable faults shown in figure 4 
are believed to have formed (or to have been reacti- 
vated, in I( bruary 1971, The soft zones, which were 
the principal evidence for the fractures, probably re- 
sulted from intergranulai movements that destroyed 
weak intergranular bonds alon^ narrow zones. These 
bonds probably are formed within a few tens of 
years by seasonal wetting and partial desiccation. 
The absence of the bonds thus suggests that the 
movements were very recent, as do the open cracks. 

Evidence of Faulting Prior to 1971, Trench A 

Two different soil features in the trench suggest, 
but do not prove, pre- 1971 faulting. The top of unit 
A, although irregular, defines in gross aspect a mod- 
erately even surface. The sharp change in elevation 
of this surface below F on figure 4 suggests deforma- 
tion ol both the surface and the buried soil after 
they formed, or alter the formation eif the soil on the 
upper part of a modified fault scarp. The trench was 
deepened at this point in a search for offset of the 
soil surface, but none was found. The inflection of 
the top of unit A does not appear in unit C, nor in 
the ground surface, and therefore is older. The con- 
figuration of unit G also may indicate pre-1971 fault- 
ing. The top of unit C consists essentially of three 
straight-line segments separated at fill D and fracture 
G. The southern segment apparently is rotated with 
respect to the other two, and the middle segment is 
vertically offset downward with respect to the north- 
ern segment. These can be seen by looking at figure 
4 almost edgewise from the south end. The ground 
surface does not show the same apparent rotation 
and offset as unit C. Thus, the apparent rotation and 
offset, which presumably resulted from faulting and 
warping, occurred before the formation of the pres- 
ent ground profile. The ground profile very proba- 



Trench Exposures Across Surface Fault Ruptures 177 



bly was considerably modified for agricultural uses 
in past decades, but not since February 9. 

Subsurface Evidence of Faulting, Trench B 

Evidence suggestive of faulting was found in the 
bedrock, at the contact between bedrock and an an- 
cient stream deposit, and at the contact between bed- 
rock and colluvium. Clear evidence of the February 
9 faulting was not found in the trench. The evidence 
is summarized below, following a brief description of 
the material revealed in the trench. 

The bedrock exposed in Trench B (unit A, fig. 6) 
is friable-to-firm sandstone, siltstone, and shale of the 
Modelo Formation. Unit B consists of loose to very 
hard, poorly sorted, moderately clean to silty sand, 
gravel, cobbles, and boulders that are interpreted as 
the deposit of an old torrential stream. Unit C is un- 
stratified yellowish-gray colluvium, consisting of fri- 
able silty fine sand that contains scattered angular to 
subangular fragments of the bedrock and rare round- 
ed-to-subangular granitic cobbles and boulders. Unit 
D is light olive gray (darker than the colluvium) 
and consists of slightly organic friable-to-firm silty 
sand that contains scattered granules and rare angu- 
lar to subangular gravel. This unit is massive, except 
for a few ill-defined zones containing a high concen- 
tration of organic matter or gravel and some layers 
of silty sand and gravel shown near point E of figure 
6. 

At two places, the bedding in the bedrock (unit 
A) steepens abruptly, suggestive of reverse-fault 
drag. One of these sharp flexures is associated with a 
steep north-dipping fault accompanied by fault brec- 



cia at least 6 cm thick; the other is adjacent to the 
very steep, probably faulted contact between the bed- 
rock and the ancient stream deposit (unit B) . This 
contact, exposed in the west wall of the trench, is 
vertical to slightly overhanging (fig. 7) . Because the 
rock at that point is highly fractured, it is very un- 
likely that a vertical-to-overhanging face could have 
remained stable long enough for the stream gravel to 
have been deposited against it. A more reasonable 
interpretation is that the bedrock was faulted against 
the already deposited stream gravel. The vertical sep- 
aration at the contact is more than 0.35 m. The 
stony colluvium above this contact is in a rather 
loose state, suggesting that a small amount of differ- 
ential movement occurred along the contact on Feb- 
ruary 9. 

A shear surface in the bedrock (at A, fig. 6) was 
traced to the contact with the colluvium, where bed- 
rock extended 0.4 m over a tongue of colluvium. Al- 
though the shear surface was not seen in the collu- 
vium, the relations strongly suggest that the bedrock 
was displaced locally over the colluvium. The shear 
surface strikes N.20°E. and dips 50°SE. Because this 
strike direction makes a moderately large angle with 
the front of the hill, faulting is a more likely cause 
of the bedrock displacement than landsliding. 

Numerous slightly open cracks dipping in various 
directions could be seen near the top of unit D after 
the trench walls had dried out; some of these may 
have been the locus of shearing on February 9, but 
the lack of distinct stratification prevented any defi- 
nite conclusion regarding shearing along the cracks. 
Mapping of a zone of discontinuous pockets and 
streaks of black, possibly manganese-stained or or- 




16 20 

METERS 



Figure 6. — Geologic section of east wall of Bartholomaus Ranch Trench B. Approximate locations of surface ruptures indicated by short 
vertical lines, such as F. Dashed lines indicate indefinite contacts. See text for further explanation. 



178 San Fernando Earthquake of 1971 
1.4 



12 



1.0 



5 1.8 
^0.6 



0.2 



Streom deposit 
B 



0.2 



0.4 




0.6 0.8 1.0 
METERS 



Figure 7. — Detail of contact between bedrock ( I) On light an/1 
stream deposit (I!) on left. Lines iii bedrock indicate bedding. 
West wall of Bartholomaus Ranch Trench II. 

ganic material near the ground surface in the vicin- 
ity of point D (fig. 6) did not show any obvious 
offsets; however, the zone is so irregular and discon- 
tinuous that no positive statement regarding offset is 
justified. 

Evidence of Faulting Prior to 1971, Trench B 

The step and locally overhanging contact be- 
tween the bedrock and the colluvium is, as discussed 
previously, suggestive of faulting. This faulting is 
not reflected in the contact between the colluvium 
and unit D and must have occurred long before 
1971, prior to formation of that contact. The proba- 
ble faulting at the contact between bedrock and the 
old stream deposit (with vertical separation of more 



than 0.55 m) would have left some dear evideu 
n had all occurred on February 9 therefore, mo 
thai faulting must have occurred before 1971 also. 



BROWN IKI \f II 

This trench wai located in San Fernando near the 
west end of the Sylmai legmenl of the San Fernando 
faull zone (1, fig. I). The trench was excavated in 
the equipment yard of general contractor C. T. 
Brown, one of the verj few open areas in the city 
crossed b\ the- fault. The trench was 29.6 rn long, 1.2 
to 1.5 rn wide-, as much as 0.1 m deep, and was ori- 
ented X.IH W. — nearly perpendicular to the trend 
of the fault zone. 

Sin face Evidence of Faulting 

The trench crossed at least one surface rupture 
and perhaps two others that were faintly visible on 
aerial photographs, but surface expression of the 
rupture was lost before the trenching. One rupture 
appeared as a moletrack about 5 cm high and 1 m 
wide, combined with a vertical displacement of 
about 8 cm, north side up, along a dirt road 5 m 
west of the trench. The moletrack scarp, which inter- 
sected the trench near point A (fig. 8) , was less 
conspicuous eastward, and its dimensions were per- 
haps 10 percent smaller at the trench than at the | 
road. 

Although the whole zone of 1971 surface faulting 
in this area was about 200 m wide (U.S. Geological . 
Survey Staff 1971, fig. 2), the principal surface dis- 1 
placements were in the southern part of the zone 
near the trench site. About 30 m north of the trench, j 
a rise in the land surface is suggestive of an old fault 




12 16 

METERS 



Figure 8.- — Geologic section of west wall of Brown Trench, showing locations of ruptures (near A, C. D, and E ) and sedimentary units. 



Trench Exposures Across Surface Fault Ruptures 179 



scarp; if so, the principal displacements in the past 
were probably north of the principal displacement 
zone of 1971 and were not intersected by the trench. 

Subsurface Evidence of Faulting 

No large fault displacements have affected the geo- 
logic units mapped in the Brown Trench, but three 
very small ruptures dipping northwest were found. 
No clear evidence of the 1971 surface ruptures was 
found in the trench. A brief description of the sedi- 
ments exposed in the trench is given below, followed 
by a description of the faults. 

Most of the sediments exposed in the trench con- 
sist of firm silty sand and clayey sandy silt (B, fig. 
8) . Although zones showing minor differences in 
grain size and sorting could be detected by detailed 
examination with a lens and by other field tests, bed- 
ding generally was not visible. The only readily 
mappable units were a gravelly silty sand at a depth 
of about 3 to 3.5 m (C, fig. 8) and a friable silty 
sand (E, fig. 8) at a depth of about 4.5 to 5 m below 
rhe surface, underlain by friable-to-loose clean sand 
and gravel. 

A barely visible fault surface was found near point 
C (fig. 8) . The fault, whose attitude is about 
N.50°E., 25°NW., shows less than 5 cm of apparent 
reverse displacement of the upper boundary of the 
gravelly silty sand. The fault could not be followed 
across the lower boundary of the gravelly sand and 
its total visible length was only 1 m. Cementation 
along parts of the fault and lack of open fractures in- 
dicate that the displacement occurred before 1971. 

A fracture near point D (fig. 8) at a depth of 3.5 
to 4 m could be traced for 1.2 m. This fracture, 
whose attitude is about N.15°E., 40°NW., appeared 
as a discontinuous series of thin, shallow, lenticular 
openings in the wall of the trench, locally showing a 
fresh-looking hairline crack. The fracture penetrates 
the lower poorly defined boundary of the gravelly 
sand, but no offset was detected. No cementation was 
noted. The open crack suggests that some movement 
occurred on February 9, but a direct connection 
with the surface ruptures of February 9 could not be 
established. 

The third rupture was found 5.5 m below ground 
surface near point E. Its attitude is approximately 
N.65°E., 52° NW., and normal separations of 4.5 and 
6 cm were measured in the wall of the trench. The 
fault, developed in sand and silty sand, could be 



traced for 0.6 m. Open fractures, voids, and cementa- 
tion were not observed. 

Evidence of Faulting Prior to 1971 

At least two of the three faults recognized in the 
Brown Trench had moved before 1971, but the dis- 
placements were very small and inconsistent in sense. 
It seems likely that these were minor subsidiary rup- 
tures and that a trench farther north across the topo- 
graphic rise would reveal a better defined and more 
important fault zone. 

OAK HILL TRENCH 

A trench dug across the Oak Hill fault by F. 
Beach Leighton & Associates in cooperation with the 
California Division of Mines and Geology (Trench 1 
of the report by Heath and Leighton, "Subsur- 
face Investigation of Ground Rupturing During San 
Fernando Earthquake" in Volume III) also was ex- 
amined by Gerald }. Eensen of the New Zealand 
Geological Survey and the author. The trench 
crossed the Oak Hill fault at the transition from 
scarp to monoclinal warp (fig. 9) . The formerly 
smooth, artificially graded surface was disrupted by 
the 1971 fault which, about 40 m west of the trench 
site, had 1.05-m reverse-slip and 0.80-m left-slip com- 
ponents of displacement (U.S. Geological Survey 
Staff 1971, pp. 68-69). 



: <fr- 










Figure 9. — Oblique aerial photograph of Oak Hill fault scarp, 
showing location of Oak Hill Trench (heavy black line). Scarp 
appears as dark ragged Hue extending from trench to road 
(upper left center). View to west. V. A. Frizzell photograph 
(date Feb. 19, 1971). 



180 



San Fernando Earthquake of l'J7l 



The trench revealed two distinct ruptures (A and 
B, fig. 10), the southernmost of which is believed to 
be the locus <>f the 1971 displacement, although the 
northernmost also may have moved ;i small amount 
;ii that time. A distinctive sand bed (C, fig. 10; is 
overlain by a wedge-shaped mixture ol poorly sorted, 
loosely compacted angulai fragments ol sandstone, 
rounded gravel, and fines (D, fig. 10). This wedge, 
because of its shape, composition, compaction, sort- 
ing, and position in relation to the northern fault 
and the rock adjacent to it, is interpreted .is <ol- 
luvium and collapsed bedrock that accumulated 
adjacent to, and shortly after the formation of, a 
scarp produced by pre 1071 movement ol the north- 
ern fault. A piece of wood was found among the 
angular pieces of rock believed to have fallen dining 
the formation of the old scarp. The wood was age- 
dated as less than 200 years old by Rubin (1971). 
The wood is possibly as much as 300 years old, but 
may be as young as 100 years old (Rubin 1072) . 

The sand bed (C, fig. 10) and the clayey silt that 
underlies it almost certainly extended a few meters 
northward across the northern fault, but the part 
north of the fault was moved upward by the dis- 
placement that produced the pre- 1971 scarp. The 
vertical component of displacement must have been 



at le;ist I m I'; move these beds out of the sec lion ex 

posed in the- trench. J bus, the fault displacement 
thai oc <m ic-d about 200 years ago and piobabJ) the 
earthquake that almost certainty accompanied it 

both gteatei than thai of I ebruai\ '). 1071. 
Although the- relations observed in the ueneh ran 
be interpreted as above, some rathei special circum- 
stances are assumed, and the given interpretation 

may not be- the correct one. One problem is the aj>- 

parent absence of conglomerate immediately north 
of fault B to supply some of the- rounded gravd 

found in the supposed collapse-rubble. This may be 
explained by postulating a thin lens of conglomerate 
immediately north of the fault to supply part of the 
rubble: conglomerate beds are exposed in the forma- 
tion north of the- fault at cither nearby points. An- 
other problem is te> explain the apparent erosion of 
some ol the sandstone immediately north of fault B 
near sand lied C, while only a bit of the soft sand 
bed was eroded. A clay seam 1 to ?> cm thick was 
noted along fault B in the lower part of the trench. 
The < las and sandstone, which could have been 
sheared and fractured adjacent to the fault, were ap- 
parently more easily eroded tfian the sand bed pro- 
tected by a capping e)| nibble. The erosion itself 
could have resulted from local concentration of run- 



4m 



- s i°PJ jvqsh and_ qr t if TcToTT 




_ 



I 

9m 



Figure 10. — Geologic section of east wall of Oak Hill Trench. Abbreviations used: cl, clay; ss, sandstone: and egl, conglomerate. The gray 
sand probably includes spoil from 1971 trenching operation which conceals upward continuation of fault A. See text for further 
explanation. 



Trench Exposures Across Surface Fault Ruptures 181 



off between the collapse-rubble and the fault scarp. 
During our field examination, Gerald Lensen and 
the author tentatively concluded that, essentially the 
entire wedge of material above the sand bed was 
rubble formed by collapse of a former fault scarp; 
however, calculation shows that insufficient volume 
of rubble would be produced by collapse, even as- 
suming 25-percent voids in the rubble and a vertical 
displacement twice as great as that which occurred 
on February 9. Thus, a composite origin by collapse, 
slope wash, and downhill creep must be postulated 
for the wedge of material overlying the sand bed. 
The age of the wood thus gives a minimum, but 
probably close, approximation of the time of forma- 
tion of the scarp. 

DISCUSSION AND CONCLUSIONS 

The following observations and conclusions re- 
garding trenching and the activity of the San Fer- 
nando fault system are based primarily on detailed 
examination of the four trenches described above, re- 
connaissance examination of seven other trenches 
across ruptures in the San Fernando area, and trench 
information reported by others (Barrows et al. 1971 
and Heath and Leighton, "Subsurface Investigation 
of Ground Rupturing During San Fernando Earth- 
quake" in Volume III) . 

The trenches show that the San Fernando fault 
system could have been identified as active by appro- 
priate investigations before 1971. The majority (9 
out of 11) of the trenches that extended below the 
modern stream alluvium and artificial fill showed ev- 
idence of faulting involving Quaternary deposits. In- 
deed, a pre- 1971 unpublished report includes a cross 
section, based on surface evidence and drilling, that 
shows bedrock faulted over alluvium just east of the 
mouth of Lopez Canyon (Geotechnical Consultants, 
Inc. 1965). The radiocarbon date on the Oak Hill 
fault indicates very recent movement there. This 
movement history can be applied to the rest of the 
San Fernando fault system because the Oak Hill 
fault is either part of the main fault or, if a subsidi- 
ary fault, it is not likely to have moved without an 
equal or greater movement on the main fault. The 
possible pre-1971 faulting of a young, near-surface 
soil horizon in Trench A on the Bartholomaus Ranch 
strengthens the inference from the Oak Hill data 
that the San Fernando fault system is very active. 



This inference is not contradicted by the fact that 
topographic evidence of young faulting is not ob- 
vious, as it is along the San Andreas fault. Topo- 
graphic evidence of young faulting is less likely to be 
preserved on a reverse fault than on a strike-slip fault 
because: (1) Active reverse faults are usually at the 
base of steep mountain fronts where vigorous chan- 
neled and sheetflood runoff and landsliding can 
quickly eradicate fault topography, and (2) the re- 
verse faulting itself produces instability both on a 
small scale at the overhanging fault scarp and on a 
large scale by oversteepening the mountain front, 
causing small and large landslides that are very effec- 
tive in obscuring fault topography. 

The radiocarbon date from the Oak Hill fault 
suggests the possibility that pre-1971 surface faulting 
occurred on the San Fernando fault zone between 
100 and 300 years ago and may have been associated 
with one of the recorded strong earthquakes such as 
that of July 28, 1769. Thus, the Holocene strati- 
graphic record along the San Fernando fault zone in- 
dicates that substantial surface faulting and damag- 
ing earthquakes may occur rather frequently on the 
fault. 

Ten out of 16 trenches across 1971 surface rup- 
tures clearly revealed the ruptures, but six trenches 
yielded no or very equivocal evidence of the rup- 
tures. Fault ruptures can be extremely difficult or 
impossible to see in massive imbedded material rang- 
ing from silt and clay to coarse bouldery sand and 
gravel. The type of material exposed thus needs to 
be considered in drawing conclusions based on the 
apparent absence of faulting in trench exposures. 

To promote recognition of faulting, trench exami- 
nations should be detailed and the walls should be 
cleaned by a technique (such as scraping, brushing, 
or picking) that is appropriate to the material en- 
countered. Geologists from several different organiza- 
tions at first agreed that no evidence of 1971 rup- 
tures was present in one of the trenches, but 
additional cleaning and close examination eventu- 
ally did reveal such evidence. Careful mapping of 
the walls can show relations not readily apparent by 
visual examination alone. 

Trenches that are too short or too shallow may 
miss important information. A trench at the mouth 
of Lopez Canyon, when it was less than 9 m long, 
missed the fault contact between bedrock and allu- 
vium that was revealed several days later when the 
trench was extended to a length of 12 m. The 



1 82 San Fernando Earthquake of 1971 



liiown Trench would have intersected no fault* il it 

had been only 3 m deep. 

Trenching confined to a particulai projecl sue 
may not reveal diagnostic relations despite use ol the 
besi judgmeni in locating the trench within the proj- 
ect. For example, two ol the trenches across the San 
Fernando lauh system showed no evidence ol pre- 
1071 latilting of Quaternary deposits, bui nine- oth 
ers did. Realistic evaluation ol the activity of a fault 
usually requires consideration of data obtained well 
outside the- confines of a particular site. 

REFERENCES 

Barrows, A.(;„ Kahle, |l . Weber, F.H., Jr., and Saul. R.I'.. 
Map of Surface Breaks Resulting From the Sim Fernando, 
California, Earthquake of February 9, 1971, Preliminary Re- 



port II Plate I, California Division ol M jn< •-, and Geology, 
Sacramento, 1971, s<.d< i : 24,000 

Geotechnical Consultants, Inc. Burbank f.aJjf 
Investigation of Tract 2H2UI. Cit) <>\ Los \ngelei Cals- 
l«, mi. i lor M< In tyre and ' > J'ark, 

(;i|j| Apr. H 1965 26 pp. (unpublished repo 

Rubin, Meyer, "S.hh|jI<- W— 2624 I G <al Sun' 

diocarbon Laboratory, Washington D.C 1971 
communis ation) 

Rubin, Meyer, "Sample W 'iu'i\ is Geological Sui\e\ Ra- 
diocarbon Laboratory, Washington, D.C, 1972 
communit ation | 

Geological Survej Staff "Surface Faulting," Tht San Fer- 
nando, California, Earthquake of lebiuury 9, 1971, geologi- 
cal Survey Professional Paper 733. IS Geological Survey 
and the National Oceanu and Atmospheric Administration, 
I S Department ol the Interior and I S Department of 
Commerce, Washington, D.C, 1971, pp. 15-76. 






Planetable Survey 

of Parking Lot Damaged 

by San Fernando Earthquake 



CONTENTS 

Page 

183 Planetable Survey 

184 Displacement Along Fault Zone 
184 References 

Publication authorized by Director, 
U.S. Geological Survey. 



JAMES B. PINKERTON 
JANE M. BUCHANAN 

U.S. Geological Survey 
Menlo Park, Calif. 



The Hubbard-Glenoaks Shopping Center, situated 
at the south corner of the intersection of Glenoaks 
Boulevard and Hubbard Street in San Fernando, was 
damaged severely during the earthquake of February 
9, 1971. The shopping center stood at the west end 
of the Sylmar segment of the San Fernando fault 
zone (U.S. Geological Survey Staff 1971, p. 57). As 
part of the preliminary work to determine the 
amount and direction of displacement across this 
zone, a planetable survey of part of the parking lot 
at the shopping center was made on February 15-16, 
1971. 

PLANETABLE SURVEY 

The survey consisted of two parts: measurement 
of elevations of selected points (table 1) and con- 
struction of a contour map (fig. 1) , and preparation 
of a sketch map (fig. 2) showing pavement cracks of 
probable tectonic origin. These pavement cracks 
could be matched to presumed tectonic ruptures in 
the ground beneath the pavement and were clearly 
not the result of sliding, buckling, and breaking of 
pavement sheets during the earthquake. 

Elevations in the parking lot were first computed 
with respect to an arbitrary datum of 100 feet. Later, 
a postearthquake spot elevation for the top of the 
sidewalk at the north corner of the Boys Market 
was obtained from the B. S. Fischer Engineering 
Company of Encino, Calif. This spot elevation was 
based on the preearthquake elevation of a bench 
mark on the northeast curb of Glenoaks Boulevard, 
73.5 feet northwest of the centerline of Hubbard 
Street. Postearthquake leveling by surveyors for Los 
Angeles city showed that the bench mark had been 
uplifted 4.8 feet (Church 1971), and this amount 
was added to the computed elevations before the 
contours were drawn. 



183 



184 San Fernando Earthquake, of l'Jl 1 



Table 1 .—Postearthquake elevations of points in Hubbard~GlenoaJu 
Shopping (:<nt<-r parking lot, San Fernanda 



Station 



El< ration 



1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 
25. 
26. 
27. 
28. 
29. 
30. 
31. 



Put* 
166.2 

166 ■<: 

163 9 

164 5 
164.1 
163.7 

163.2 

163.1 

162.8 

162.6 

162.2 

161.9 

168.3 

163.9 

164.1 

163.3 

U,2. 

161 

164. 

162. 

160.8 

159.7 

161.3 

156.3 

160. 

161. 

164. 

165. 

162. 



* The elevations are based on postearthquakc preliminary releveling 
(by Los Angeles city) of bench mark on northeast curb of Glenoaks 
Boulevard, 73.5 feet northwest of centerline of Hubbard Street. Spike 
is in curb. Preearthquake elevation was 1,170.804 feet; postearth- 
quake elevation is 1,175.604 feet (+4.8 feet). All elevations are 
rounded to nearest one-tenth of a foot. 

** The computed elevation of station 21 is anomalously high and 
was disregarded when the contour map (fig. 1) was drawn. 

DISPLACEMENT ALONG FAULT ZONE 

According to earlier reports (U.S. Geological Sur- 
vey Staff 1971, p. 57) , displacement along the Sylmar 
segment of the San Fernando fault zone consisted of 
uplift and horizontal (primarily left-lateral) offset 
along a steep, north-dipping plane. A narrow band 
of shearing and thrusting on the south was flanked 



by a wide band of extension on the north 
displacement occurred in both hands, hut about 
one-hall of the vertical and virtually all of the bori* 
zonal displacements were confined to the narrow 
shear-thrust /one on the south. 

I lie results of our survey agree with these general 
observations, Comparison of the postearthquake and 
uilifjii.de maps of the parking lot (figs. 1 and 
3) shows that despite the number and complex 
the ciacks, the parking lot sulfate was not deformed 
significantly. Profiles drawn along the axis of the 
drainage trough and along the sidewalk (fig. 4) indi- 
cate that the sulfate was uplifted and tilted south- 
uaid. I he t ia< ks show a stepwise northward increase 
in vertical displacement (fi^. 2), and figure 5, on 
which points ol equal uplift are plotted, clearly 
indicates that the amount of vertical displacement 
in< leased northward and was spread across the entire 
fault zone. Most of the tracks showed no lateral 
offset, but those that did generally showed a small 
light-lateral component. Differences between the pre- 
earthquake and postearthquake positions of the 
buildings and sidewalks on figures 1 and 3 may stem 
from lateral displacement, but it is more likely that 
these differences reflect errors in horizontal measure- 
ment. More than 1 m ol left-lateral displacement 
was measured on the main shear-thrust zone in this 
area (Clark 1971), but this displacement is not 
reflected in our survey because no stations were 
pic ked south of the shear zone. 

REFERENCES 

Church, J. P., U.S. Geological Survey, 1971 (personal com- 
munication) . 

Clark, M.M.. U.S. Geological Survey, 1971 (written communi- 
cation) . 

U.S. Geological Survey Staff. "Surface Faulting," The San 
Fernando, California, Earthquake of February 9, 1971, Geo- 
logical Survey Professional Paper 733, U.S. Geological Sur- 
vey and the National Oceanic and Atmospheric Adminis- 
tration, U.S. Department of the Interior and U.S. Depart- 
ment of Commerce, Washington, D.C., 1971, pp. 55-76. 



Planetable Survey of Parking Lot 185 




■ i 



Contours from planetable survey, 

February 15-16,1971. Alidade, J. M. Buchanan; 

rod, J B Pinkerton. Contoured by Pinkerton 



Figure 1. — Contour map of postearthquake surface, Hubbard-Glenoaks Shopping Center parking lot, San Fernando, Calif. 



18f> San Fernando Earthquake of J 97 J 




Cracks mopped by J B Pmkerton. 
Februorf I5-I€, 1971 



Figure 2. — Sketch map showing ruptures in the northeastern part of Hubbard-Glenoaks Shopping Center parking lot. 



Planetable Survey of Parking Lot 187 




NORTHWEST 





1170 


" 15 


-— . -^^_l 


Posteortfiquoke 
^'profile 








Rod station 






1 160 
1155 




Preeorthquake 


profile 




22 




/ 
28 x 


P'OK<ntd io plono 
of profile) 












X 


1150 
( 




















*■ 


i 


50 


100 


150 




200 




250 


300 



o NORTHWEST 



DRAINAGE TROUGH 



1 170 












1165 


3^ 


^ Rod stations 

1 proiecied lo plonf ^\ 

of p.ol.iel ^10 


13 


23 


Postearthqooke 
/profile 








1160 












1155 




Preearthquake profile ' 








1150 













150 200 250 

Horizontal distance, m feet 



Peterson, orchilect, December 4, 
1961, far the Hubbord - Glenooks Shopping 
Center Job No 61-126, Shoot A-l 



Figure 4. — Preearthquake and postearthquake profiles of sidewalk 
and drainage trough, Hubbard-Glenoaks Shopping Center. 



Figure 3. — Contour map of preearthquake surface, 
Hubbard-Glenoaks Shopping Center parking lot. 




EXPLANATION 



Point ot intersection of pre- and 
postearthquake contours, showing 
amount of upl'ft, 10 feet 



Figure 5. — Map showing points of equal uplift in 
Hubbard-Glenoaks Shopping Center parking lot. 



Ground Displacement 

at San Fernando Valley Juvenile Hall 

During San Fernando Earthquake 



CONTENTS 




Page 






189 


Introduction 




190 


Zone of Displacement 


191 


Geologic and 


Soil Conditions 


194 


Conclusions 




196 


References 





RICHARD B. FALLGREN 
JAY L. SMITH 

FVGRO, Inc. 

Consulting Engineers and Geologists 

Long Beach, Calif. 



INTRODUCTION 

The San Fernando Valley Juvenile Hall was dam- 
aged severely during the earthquake of February 9, 
1971. Although located in a region of moderate to 
heavy damage (Modified Mercalli intensity VIII + ) , 
the destruction at the Juvenile Hall was unusually 
severe because of the ground displacement through- 
out the facility. An investigation conducted for Los 
Angeles County has determined that local soil and 
geologic conditions were responsible for the displace- 
ments and the concentration of damage to structures 
at this facility (Fallgren and Smith 1971) . 

The Juvenile Hall is a Los Angeles County juve- 
nile-detention facility located in the Sylmar district 
north of San Fernando Road (fig. 1) . The site is ap- 
proximately 7 1/ 2 miles south of the epicenter of the 
February 9 earthquake and 2i/£ miles northwest of 
the known surface ruptures along the Sylmar seg- 
ment of the San Fernando fault. The facility was 
constructed in 1962 on the 30-acre site and involved 
the removal of an existing olive grove, with subse- 
quent grading to produce a multilevel site using cuts 
and fills as much as 15 feet deep. 

Structures on the site include numerous one- and 
two-story school and dormitory buildings, with con- 
crete frame or reinforced masonry bearing walls and 
concrete floors and roofs. Foundations consist of shal- 
low spread footings supported on at least 2 feet of 
compacted fill. Most of the buildings are around the 
perimeter of the site, and many split-level buildings 
are connected. Interior areas of the site are devoted 
to athletic fields and landscaping, and the facility is 
enclosed entirely by a 10-foot-high concrete block 
wall. 

Damage to the facility occurred as the result of se- 
vere shaking and differential ground movement. 



189 



190 



San Fernando Earthquake of li>71 



rnoTHIlL BOULEVARD 




Figure 1. — Vicinity map — San Fernando Valley Juvenile Hall. 

Heaviest damage to buildings occurred in the vicin- 
ity of the permanent ground displacements. The 
ground displacements across the Juvenile Hall site 
were first identified and described by Youd (197 hi) . 
Preliminary studies indicated that ground movement 
on the site was related to a larger zone of ground dis- 
placement extending southwestward to the shore of 
Upper Van Norman Reservoir. 

ZONE OF DISPLACEMENT 

The limits of the zone of displacement are indi- 
cated approximately by the pattern of ground sur- 
face ruptures shown in figure 2. The zone is approx- 
imately 4,000 feet long and about 900 feet wide (at 
its maximum width) . It extends from a point 500 
feet northeast of the Juvenile Hall to within the Syl- 
mar Converter Station site at the edge of Upper Van 
Norman Reservoir. The ground surface descends ap- 
proximately 40 feet in elevation along the length of 
the zone, resulting in an average slope of about I 
percent from the northeast. Major lateral movement 
within the zone was downslope in a southwest direc- 
tion. 

The north boundary of the zone bisects the Juve- 



nile Hall site, crowing the lacjhtv through the 
kitchen, medical, and court buildings (fig 
Ground ruptures along this boundary indicate right- 
lateral slip, and the trend ol majoi c tacks is gener- 
ally parallel to the direction of movement ol the dis- 
placed /one. The south boundary ol the 
displacement rone < tosses the southeast cornei ol the 
Juvenile Hall site through the maintenance an': 
ply building. Ground ruptures along tins boundary 
are characterized by left-lateral slip, and the I 
(tacks generally trend nearly north-south in en eche- 
lon pattern, approximately 45" to the directi< 
gross movement. 

1 he amount ol relative lateial movement within 
the /one is shown m figure '<. I he lateral movement 
shown represents offsets of curbs and property lines 
crossing the /one, as measured by the California Di- 
vision ol Highways, the Los Angeles Department oflj 
Watei and Power, and the Los Angeles County Engi- 
neer. This survey information indicates that as much 
as 5 feet of relative lateial movement has occurred 
on the Juvenile Hall site. The same magnitude of* 
relative movement has occurred to the southwest as 
far as Sepulveda Boulevard, adjacent to the converter 
station. However, beyond the drainage channel 
which separates the converter station from Sepulveda 
Boulevard, the lateral movements measured were nc 
greater than about 2 feet. 

Exploratory trenc lies across the boundaries of the 
zone of displacement within Juvenile Hall anc 
southwest of San Fernando Road allowed examina 
tion of the cracks at depth. In general, the crack: 
were found to die out and to curve inward witl 
depth toward the interior of the zone of displace 
ment. The diagram of the trench shown in figure L 
represents the conditions encountered in a nearb 
north-south trench excavated across the north bound 
ary of the zone of displacement on the Juvenile Hal 
site. The largest crack coincides with a 7-inch verti 
cal displacement of the ground surface, with under 
lying soil contacts being similarly displaced. Near th 
bottom of the trench, however, the crack i 
coincident with a displaced soil-contact that has al 
most twice the amount of offset of higher strata. L 
view of the lateral continuity of the boundaries c 
the involved soil horizons, such a difference mu; 
represent evidence of prior displacement. Narroi 
vertical zones of soft soil, truncated by upper hor 
zons of alluvium and fill soil, also were disclosed i ' 
the trenches. Because vertical displacements of th 



Ground Displacement at San Fernando Valley Juvenile Hall 191 




Figure 2. — Location of ground surface ruptures in zone of displacement. 



horizons are not apparent, these zones most likely 
^present loosely rilled tension cracks produced by 
pisodes of displacement before 1971. 

GEOLOGIC AND SOIL CONDITIONS 

The Juvenile Hall site is near the mouth of Grape- 
vine Canyon, a south-draining valley of the San 
Gabriel Mountains (fig. 5) . This valley and others 
mmediately to the east and west have been eroded 
into sedimentary rocks to produce steep-flanking 
ridges and gently sloping alluvial fans. The alluvial 
material has accumulated in a depression between 
'the San Gabriel Mountains and the Mission Hills. 
This depression has a northeast-southwest trend and 
generally follows the projected trend of the Mission 
(Hills syncline (Merifield 1958) . 

The east-flanking ridge of Grapevine Canyon ex- 
tends into the northwest corner of the Juvenile Hall 
site and descends beneath the alluvium that fills the 
northeast-trending depression. The ridge is com- 



posed of siltstone, sandstone, and conglomerate of 
the Saugus Formation. The location and maximum 
depth to bedrock beneath the Juvenile Hall site and 
in the central part of the depression are unknown, 
but are at least 100 feet beneath the Juvenile Hall, 
and the depression undoubtedly bottoms in the Sau- 
gus Formation. 

The alluvium beneath the Juvenile Hall site exists 
as fans, developed during late Pleistocene and Holo- 
cene time, at the mouth of Grapevine Canyon and of 
smaller valleys immediately east. This material was 
deposited chiefly by torrential streamflow with occa- 
sional deposition by mudflow. Large composite fans 
have also developed below Sombrero and Weldon 
Canyons, and below other smaller tributaries. As a 
consequence of the merging of several fans, a low- 
land has developed at their intersection with the 
Mission Hills and occupies the area between Juve- 
nile Hall and Upper Van Norman Reservoir. 

Two northeast-trending faults have been recog- 
nized in the San Gabriel Mountains immediately 



192 San Fernando Earthquake of 1971 




OLIVE SWITCHING 
STATION 



Figure 3.— Relative lateral ground movement in zone of displacement. 



m 



/ 



'/AJ9 OWKTS 



60 
I 



Very narrow cracks 

Sandy Silt, 
J dry, hard 
_ Sandy Silt, pOTOU 
very stiff, dry 

- Silty Sand, brown w/scal 
streaks sand, si, porous 
Sand & Gravel, grej 
Sandj Silt, ligiit brown 
firm, slightly moist 

Sandy Silt, grey-brown, firm, 
moist, slightl) porous 

Sandy Silt, dark brown, 



Trend oi crack N40E 




[St, porous 
Silty Sand, very dark brown with some gravel 



TRENCH 1 



Figure 4. — Exploratory trench across ground ruptures on Juvenile Hall site. 

above the Olive View Hospital. These are the Olive 1971). A careful examination was made of the hill- 
View and North Olive View faults (Merifield 1958 side exposure of these faults after the earthquake of 
and Proctor 1968). Projections of these faults to the February 9. Although irregular and discontinuous 
southwest through the Juvenile Hall site have been cracks associated with slumping on steep slopes exist 
made by Merifield (1958) and Proctor (1968 and in many nearby places, no evidence was observed oi 



Ground Displacement at San Fernando Valley Juvenile Hall 193 




Note: Shading denotes approximate areas of alluvial fans 

Figure 5. — Topography as shown on 1935 Sylmar Quadrangle. 



slip on the Olive View and North Olive View faults 
during the San Fernando earthquake. Trenches 
across the zone of displacement within and outside 
the Juvenile Hall site disclosed no evidence in the 
upper 15 feet of alluvium of an offset lithology at- 
tributable to slip on a fault. Survey data, obtained 
from the U.S. Geological Survey at the time of our 
investigation, indicated that there has been no net 
relative displacement in the vicinity of the Juvenile 
Hall and Sylmar Converter Station outside the dis- 
placement zone (Youd 19716). 

Because evidence of fault movement had not been 
found on the surface exposures or in shallow 
trenches, it was our opinion that tectonic slip did 
not occur on the Olive View and North Olive View 
faults. The U.S. Geological Survey has, however, re- 
cently reported finding a small right-lateral displace- 
ment across the zone of displacement based on re- 
survey data (see the paper by Youd, "Ground 
Movements in Van Norman Lake Vicinity During 



San Fernando Earthquake" in Volume III) . This 
movement may be related to displacements across 
faults in the underlying rock during the earthquake 
of February 9. Detailed postearthquake mapping (by 
the California Division of Mines and Geology) of 
the hills immediately above Olive View Hospital has 
disclosed an approximately 1-inch vertical displace- 
ment of the around surface, with a thrust-sense of 
slip that developed across a shear in bedrock that 
could be interpreted as evidence of faulting (Weber 
1971). At this date, it is our opinion that tectonic 
slip, if any, on the Olive View and North Olive 
View faults was minor and did not influence the dis- 
placement of the ground at Juvenile Hall. 

The properties of alluvial soils in the vicinity of 
the Juvenile Hall were investigated by means of 
bucket-auger borings up to 80 feet deep. The 
soil profile along a section line crossing the Juvenile 
Hall site from northwest to southeast is shown in 
figure 6. This section is taken along a line transverse 



194 San Fernando Earthquake of 1 07 1 



1320 

i 100 
1280 

1260- 
1240 
1220 
1200 



l[ 

Original \ ind surbi - 

. i 




Saugu i i V - 

\\ Medium di m ■ sill 



V- 



T>. 








■ j j 

- 

■ - - 




\ ■ 

AIJh . 



SECTION A -A' 



Figure 6. — Geologic and soil profile across Juvenile Hall site. 



- 



II 












to the direction of movement within the /one ol dis- 
placement. The sand and silt soils indicated are typi- 
cal of soils to be expected near the terminus of al- 
lnvial fans merging in a lowland. The significant soil 
feature, however, is the existence of a /one ol soft, 
saturated soil underlying the dense, dry upper soils. 
Soils in the soft /one consist of sandy silt and uni- 
form fine sand. A similar profile of soil consistency 
was disclosed as a result of a penetrometer survey by 
the California Division of Highways (Marek 1971) 
along the Golden State Freeway (fig. 7) . 

The depth to ground water in the vicinity of the 
Juvenile Hall is shown in figure 8. The contours in- 
dicated are based on data from the recent bucket-au- 
ger borings and from nearby wells. The ground-wa- 
ter surface generally conforms to the topography, 
being nearest to the ground surface in the low area 
south of the Juvenile Hall. 



CONCLUSIONS 

The permanent ground displacements in the vicin- 
itv ol the Juvenile Hall are the result of settlement 
and gradual migration ol solt soils downslope in a 
/one ol narrow lateral extent during the earthquake. 

I he /one exists here as the combined effects ol 1 
selective deposition ol solt soils in a lowland or 
trough formed by coalescing alluvial fans in a bed- 
rock depression; (2) near-surface ground water; and 

(3) past displacements of similar nature in the same 
area. The Olive View and North Olive View faults 
pass through or near the displacement /one, but tec- 
tonic slip on them probably did not occur on Febru- 
arv 9. The presence of the faults, and their past dis- 
placement of the ground surface during late 
Pleistocene and Holocene time, may have contrib- 
uted to the formation of the depression containing 




SECTION D-D' 



Figure 7. — Soil profile along Golden State Freeway as indicated by penetrometer survey. 



Ground Displacement at San Fernando Valley Juvenile Hall 195 




EASTERN PORTION SYLMAR 
GROUND WATER BASIN 



LEGEND 

I | Qal | QUATERNARY ALLUVIUM 
/ JQTs \ SAUGUS FORMATION 

BASEMENT COMPLEX 
WELL SHOWING DEPTH TO WATER 



• SOIL BORING SHOWING DEPTH 

" z TO WATER 



Figure 8. — Depth-to-water contours (by Glenn A. Brown & Associates, Sept. 1971). 



the soft soils, but in the Juvenile Hall area it is not 
likely that the past tectonic slip on the faults signifi- 
cantly changed the strength characteristics of the soft 
soil. 

A generalized soil profile near the center of the 
displaced zone, based on the borings, consists of 20 
feet of medium dense and moist soil overlying a 10- 
foot-thick layer of soft and saturated soil. The re- 
sponse of this soil model to lateral forces generated 
by the earthquake would result in large, nonelastic 
shearing strains throughout the depth of the soft soil 
layer. It is estimated that shear strain in this layer 
during the San Fernando earthquake resulted in a 
maximum net dovvnslope lateral displacement of the 
ground surface of the order of 3 inches during each 
cycle of strong shaking. The San Fernando earth- 
quake produced about 20 cycles of strong shaking. 
Therefore, a total ground-surface displacement of 
about 5 feet can be accounted for by this explana- 
tion. Displacements away from the center of the zone 



of movement were less, depending on the thickness 
and consistency of the soft layer. The net lateral dis- 
placement in the direction of Upper Van Norman 
Reservoir was caused, in part, by the slight topo- 
graphic slope in that direction and, in part, by the 
lesser degree of lateral support in that direction at 
the drainage channel. 

The location and size of ground ruptures along 
the boundaries of the zone of displacement are re- 
lated to the existence of relatively brittle surface 
soils, both natural and fill. The natural surface soils, 
where exposed on the Juvenile Hall site, consist of 
hard, dry, and slightly cemented clayey sand to a 
depth of several feet. An exposure of this condition 
is shown in figure 9 where the underlying softer soils 
have been consolidated by the blast from a small dy- 
namite charge during a seismic refraction survey. 
The fill soils are also brittle compared to the moist 
deeper soils. Long and relatively continuous ground 
ruptures along the north boundary of the displace- 



196 



San Fernando Earthquake <>\ 1971 




Figure 9. — Crater resulting from consolidation of soft soil 
by small dynamite blast during seismit refraction survey. 

mew zone are generally found in the crustlike soils 
described above. Surface ruptures along the south 
boundary are shorter and less well-developed, tend- 
in" toward an en echelon pattern because ol the lack 
of brittle surface soils. 

Some saturated soils in the zone of displacement 
consist of uniform fine sand which has a potential 
for liquefaction during strong shaking. It is quite 
likely that local liquefaction of these soils during 
the earthquake contributed to ground instability and 
subsequent displacement. The existence of sand boils 
in the high ground-water area southeast of Juvenile 
Hall (fig. 2) is evidence of this local liquefaction. 
However, soils with liquefaction potential are not 
sufficiently widespread throughout the zone of dis- 
placement to account for the lack of stability of the 
area during the earthquake. The soft and loose satu- 
rated soils have sufficiently low strength under static 
conditions to account for the lateral and downslope 
ground movement during strong shaking. Large-scale 
liquefaction would have resulted in much greater 
displacements. It may be concluded, therefore, that 
liquefaction played a minor role in the performance 
of the site during the earthquake. 

Our investigation indicates that future ground dis- 



placements undei seismic condition*! < an be 

to remain confined to the zone ol displacement that 

developed during the San Fernando earthquake. 

J his conclusion is based on the lateral extent ol the 
soli soils responsible lor the movement and on 
logic evidence thai past displacements ha\e oc< 
along this same zone I he- evidence indicates that an 
en thquake with characteristics similar to those of the 
February 9, 1971, earthquake could be- expected to 
produce ground displacements across the Juvenile 
II all site, following the same path and pattern and 
ol about the- same- magnitude as those caused bv 
that eai thquake. 

REFERENC1 S 

Fallgren, Richard B.. and Smith. J;: /logic and Soil 

Investigation, S;m Fernando Juvenile Hall, Sylmar, Cali- 
fornia." for the Los Angeles County Engineer b% H.'GRO, 
Inr . Long Beach, Calif., Sept. 20, 1971, 45 pp. and 2 pi. 
(unpublished report) . 

Marek, (.1 California Division of Highways, Sacramento, 
Sept. 1971 (written communication) . 

Merifield, P.M., "Geology of a Portion of the Southwestern 
San Gabriel Mountains. San Fernando and Oat Mountain 
Quadrangles. Los Angeles County, California." M. A. thesis, 
University ol California, Los Angeles, 1958, 61 pp. 

Proctor, R.J., "Geologic Map and Section Along the 5. 5-Mile 
San Fernando runnel." No. L— 1078, Metropolitan Water 
District of Southern California, Los Angeles, 1968, scale 
1:12.000 (unpublished). 

I'roetor, R.J.. "Geologic Map and Section Along the 5.5-Mile 
San Fernando Tunnel." No. L-1078 (revised), Metropolitan 
Water District of Southern California, Los Angeles, Feb. 26, 
1971, scale 1:12,000 (unpublished). 

Weber. H.. California Division of Mines and Geology. Sacra- 
mento. Sept. 1971 (personal communication). 

Voud, T. Leslie, "Landsliding in the Yicinitv of the Van Nor- 
man Lakes," The San Fernando, California, Earthquake of 
February 9. 1971, Geological Survey Professional Paper 733, 
U.S. Geological Sur\ev and the National Oceanic and At- 
mospheric Administration. U.S. Department of the Interior 
and U.S. Department of Commerce, Washington, D.C., 
1971a, pp. 105-109. 

Voud, T. Leslie, U.S. Geological Survey, Menlo Park, Calif.. 
Aug. 19716 (personal communication) . 



Ground Movements in 
Van Norman Lake Vicinity 
During San Fernando Earthquake 



CONTENTS 


Page 




197 


Introduction 


198 


Surficial Features 


198 


Survey Results 


203 


Subsurface Conditions 


205 


Origin of Rupture Zones 


205 


Acknowledgments 


206 


References 



Publication authorized by Director, 
U.S. Geological Survey. 



T. LESLIE YOUD 

VS. Geological Survey 
Menlo Park, Calif. 



INTRODUCTION 

Rupturing and shifting of the earth's surface oc- 
curred at several locations on very gentle slopes in 
the vicinity of Van Norman Lake (commonly called 
Upper Van Norman Reservoir) during the 1971 San 
Fernando earthquake. The precise origin of these 
ruptures and displacements has been the subject of 
some controversy. A landslide origin has been pro- 
posed by Youd (1971) who recognized, nonetheless, 
that some differential tectonic displacements could 
have occurred. This view is also generally shared by 
the Metropolitan Water District of Southern Cali- 
fornia (MWD) staff (see paper, "Geology, Earth- 
quake Damage, and Water Table Fluctuations — ■ 
Metropolitan Water District Facilities, Sylmar Area" 
in Volume III), but others (Crandall 1971 and 
Slosson 1971) have suggested that the ruptures, at 
least those northeast of the lake, were probably 
the result of deep-seated fault movements. Still oth- 
ers, while agreeing that the features northeast of the 
lake were nontectonic, concluded that they were 
formed as the result of compaction of subsurface sed- 
iments (Scott 1971) or downslope migration (Fall- 
gren and Smith 1971) rather than by landsliding. 

This study was made to determine the origin of 
the ruptures and displacements in the Van Norman 
Lake vicinity and to obtain more information about 
the phenomena that occurred there. Surficial features 
were mapped, points with known preearthquake lo- 
cations surveyed, and subsurface data gathered. The 
results show that differential displacements were 
smaller outside rupture zones than inside and that 
relative horizontal displacements within rupture 
zones were downslope and generally several times 
greater than corresponding vertical displacements. 
Soft soil layers or potentially liquefiable layers were 



197 



198 



San Fernando Earthquake of 1971 



found .it relatively shallow depths beneath the 'lis 
turbed /ones. It is concluded thai landsliding, pre 
dominantly of the lateral spreading type (Varnes 
1958), was the immediate cause ol the ruptures and 
differential displacements that occurred neai Van 
Norman Lake. 

SURFICIAL FEATURES 

The ruptures were confined to a northeast-trend- 
ing hand which extended from the Van (»<>gh Street 
Elementary School on the southwest to the olive 
groves east of the San Fernando Valley Juvenile Hall 
on the northeast. The more significant niptures are 
plotted on figure 1. Van Norman Lake effectively 
divides this hand into two /ones, one on each side ol 
the lake. In each /one, the ruptures formed in allu- 
vium or in fill overlying alluvium. 

Northeast of the Van Norman Lake, the ruptures 
hounded a tongue shaped area that extended about 
4,000 feet upslope from the lake. The zone was as 
much as 1,300 feet wide southwest of San Fernando 
Road, but was only about 900 feet wide farther 
downslope at the Golden State Freeway. The average 
slope between the lake (1,220-ft elevation) and the 
upper margin of the zone ( 1 ,280-ft elevation) is 1.5 
percent. Near the lake and near the upper margin, 
the slope is locally greater; through the midsection, 
the slope is only about 0.9 percent. 

Ruptures with right-lateral displacement formed 
on the north margin of this zone; ruptures with left- 
lateral displacement formed on the south margin; 
and extensional ruptures formed at the northeast 
margin. These ruptures and displacements were re- 
sponsible in large part for the considerable damage 
to constructed works located within this zone 
(Moran 1971, Thompson 1971, Youd 1971, and 
YoudandOlsen 1971). 

Sand boils erupted at several locations on or near 
the disturbed zones (fig. 1) . Two groups of sand 
boils were exposed on the lake bottom after the 
water was drawn down, one in the eastern lobe of 
the lake generally on line with the southern part of 
the rupture zone and the other in a band through 
the north and northwest sectors of the lake. Sand 
boils also erupted on the Joseph Jensen Filtration 
Plant fill near the southern margin of the rupture 
zone and along the base of the fill about 500 feet 
west of the lake. Other sand boils erupted at the base 
of the Sylmar Converter Station fill about 200 feet 



cast ol the laic; a single boil was found 2(K 
of the freeway neai the southern margin ol i 
approximately 50 boils erupted on th<- ruptun i 
in the (i<ld between San Fernando Road and tt ■ 
completed freeway access tamp: anothei group 
found al the base of the railroad embankment south 
ol the Juvenile Hall. 

West ol the lake, the rupture /one extended 3,000 
feel from the lake to the Van Gogh School. Tl 
i slope between these two locations is abot 
pen (in. I he i upture /one was as mu( h feet 

wide on the eastern segment of the Joseph Jensen Fil- 
tration I'lant fill. Displacements on these ruptures 
were mainly \eiti(al oi extensional in a downslope 
dire< tion. 

The partly completed filtration plant suffered con- 
siderable damage from rupturing and displacements 
(Duke 1971). Other damage included disrupted 
pipelines and pavements at several locations, a frac- 
tured and offset flooi slab in a house, and fractured 
foundations and floor slabs at the Van Gogh School. 

Ruptures, lateral and vertical displacements, and 
sand boils also occurred in recent alluvium in and 
near the upper reaches of Lower Van Norman Lake. 
These disturbances caused no significant damage. 

SURVEY RESULTS 

The magnitudes and locations of displacements as- 
sociated with the earthquake in the area surrounding 
the rupture zones were determined by comparing 
postearthquake coordinates and elevations of survey 
monuments within the subject area to those estab 
lished before the event. The preearthquake positions 
of the monuments are plotted on figure 1. The 
preearthquake elevations and coordinates were estab 
lished, or rechecked, in nearly all cases since 1963 by 
other agencies, including the National Geodetic 
Survey (NGS) of the NOAA National Ocean Sur- 
vey, 1 the Los Angeles City Bureau of Engineering 
(LABE) , and the Los Angeles Department of Water 
and Power (LADWP) . Postearthquake elevations 
are from releveling by LABE (February to March 
1971) using a point at the intersection of Van Nuys 
and Foothill Boulevards, one-half mile south of the 
San Fernando fault zone, for reference. Postearth- 
quake coordinates are based on surveys by LADWP 
(February to April 1971) and the U.S. Geological 
Survey — USGS — (June 1971) and were later unoffi- 



i Formerly U.S. Coast and Geodetic Survey. 



Ground Movements in Van Norman Lake Vicinity 



199 



1280 * 



<r 



Bri -. Ml *, 0.7? up 

stl one &_» io.79.pi_ } 

IO.I3N,0.59E,0.32p(i)i A^ \^' 



l 



0^ 







£q 






POL 
(0.18 N, 0.41 £ 



Vor* Gogfi 
Schoot 



$ 1/ 




.SYL A 12 B •> \\ 

X^N93S, 2 63 E I I ) 

•I A WP3 



^ 




BENDIX 

j 4 N, 0.02 E, 170 up! 



EXPLANATION 



Left- loie roi displacement, in feet 

0.8 fl 
Right-lolerol displacement, in feet 

& 

Survey poml 








*ii 



10.21 S. l.07E,2.22up) 
Displacement vector and components 
ot displacement in fee) 



DISPLACEMENT SCALE 



5YL 012 8 




MAP SCALE 






\f^ 



Figure 1. — Map of Van Norman Lake vicinity, showing locations of ruptures generated by earthquake and survey monument locations. 
Horizontal displacements shown are in relation to SYL C11C, and elevation changes are in relation to external LABE reference point. 
(Revised and updated version of fig. 1, Youd 1971.) 



cially adjusted by the author to the constrained ad- C11C moved north 0.54 foot, moved west 1.34 feet, 

justment of coordinates established by NGS. and rose 1.97 feet. To show more clearly the differ- 

A comparison of preearthquake and postearth- ential horizontal displacements in the area, the hori- 

quake data shows tentatively that monument SYL zontal displacements relative to monument SYL 



200 



.San Fernando Earthquake of 1971 



C11C, rather than absolute horizontal displacements, 
were plotted on figure 1. (To obtain the tentative 
absolute movement, one need only add algebraically 
the components given above foi SYL C11C to the 
components given in parentheses foi each station on 
fig.l.) 

Monument SYL B11B may have been disturbed 
alter the earthquake. It was located beneath a badly 
damaged freeway overpass that was dismantled and 
replaced before the resurvey was made. Because the 
stability of SYL B11B is questionable, two other 
points, a lead and tack at the northeast entrance to 
the converter station (CSN) and a nail at station 
149 + 00 on San Fernando Road (1 19) . were used to 
give additional control for that area. Also, station 
POL, a spike and tin on Balboa Boulevard, was 
added to provide a control point for that area. 

Outside the rupture /ones, the displacement vec- 
tors appear to define at least two separate units oi 
crustal blocks that moved relative to each other dur- 
ing the earthquake. The first block, south of the Ju- 
venile Hall, remaining essentially fixed with respect 
to SYL C11C, includes SYL C11C, Park, WP3, 
Bendix, and SYL D12B. The second block, west of 
the Juvenile Hall, contains stations CSN, SYL Bl IB, 
149, and possibly POL, Mack, and Grapevine. This 
block appears to have moved northeast or right later- 
ally with respect to the first block, possibly across the 
Olive View fault (Merifield 1958 and paper by 
MWD, "Geology, Earthquake Damage, and Water 
Table Fluctuations — Metropolitan Water District 
Facilities, Sylmar Area" in Volume III) , which is 
inferred to trend northeastward approximately be- 
neath the rupture zone (fig. 1) . At the Juvenile 
Hall, the relative displacement across the inferred 
fault is about 0.4 foot (between stations WP3, Park, 
and SYL C11C on the southeast and stations CSN 
and 149 on the northwest) , so that the distance be- 
tween 149 and SYL C11C was shortened by 0.32 
foot. This compression probably caused the spectacu- 
lar bowing and buckling of the railroad tracks that 
occurred between these two points during the earth- 
quake (Scott 1971, fig. 4.15) . It is of interest to note 
that the approximately 0.31 foot of rail removed in 
repairing the tracks (Clark 1971) was almost equiva- 
lent to the shortening of distance between 149 and 
SYL C11C. 

The vector displacements of SYL B11C and SYL 
A12B, located within the rupture zones, clearly differ 
either in magnitude (SYL A12B) or direction of 



movement (SYL I.IK, from those displacements o| 
nearby stations located outside the disturbed / 
Furthei data on movements within the rupture z 
were obtained b\ resurveying other previous! 
points, such as nails set on highway stations, c on- 
struction control points, and points on property 

lines. Data from the COnvertei station were supplied 
by LADWP, while the othei points were sin veyed by 
USGS using a radial-line traverse procedure. 

Additional displacement data came from offset 
measurements ol the cast and west fences at the 
convertei station b\ LADWP, the curb line of San 
Fernando Road by I W'A and the noith-soiitli axis 
of the- filtration plant b\ \1\VI). The displacement 
vectors on the extension of Yarnell Street between 
Bradley Avenue and San Fernando Road are from 
direct-distance measurements between a set of nails 
placed before the earthquake by I.ABF and a similar 
set placed after the event. 

Displacement vectors ('adjusted to nullify the in- 
fluence of the displacements in the area surrounding 
the rupture /ones; and offset measurements are plot- 
ted in figure 2 for the area northeast of the lake and 
in figure 3 for the area west of the lake. Northeast of 
the lake, the horizontal displacements form a well-de- 
fined pattern in which the margins of the displace- 
ment /one correspond closely to those of the rupture 
zone. In every instance, displacement was downslope, 
although in some local areas a component of cross- 
slope displacement also occurred. 

Horizontal displacement within the zone of failure 
increased downslope from zero at the upper margin 
of the zone to a maximum of 5.7 feet at San Fer- 
nando Road. At the extension of Yarnell Street, the 
maximum was 1.8 feet. Between San Fernando Road 
and the east fence of the converter station, the maxi- 
mum displacement appears to have been essentially 
constant: 5.1 feet at the freeway and 5.0 feet at the 
east fence. 

A discontinuity in the horizontal displacement 
pattern occurred across the approximately 8-foot- 
deep flood control channel between the east fence of 
the converter station and a group of A-frames and 
transformer pads west of the channel, whose maxi- 
mum measured displacement was about 0.7 foot. 
Thus, more than 4 feet of horizontal displacement 
was absorbed by the channel. This compression se- 



2 An offset is the perpendicular distance from the relative pre- 
earthquake position of a linear feature, such as a curb or fence, to 
the postearthquake position of a point on that feature. 



Ground Movements in Van Norman Lake Vicinity 201 




E X PL ANATION 
Vector displacement 

Offset displocemei.. 



Surfoce rupture 







5 10 Feet 

1 . i 


DISPLACEMENT SCALE 


-Zl. 










i 


1000 FEET 
, . i j i 






MAP SCALE 



Figure 2. — Rupture zone northeast of Van Norman Lake, with horizontal displacements superimposed. 



verely disrupted the concrete lining and visibly offset 
the east bank, of the channel (Yond and Olsen 1971, 
fig. 2) . The invert of the channel also heaved as 
much as 2 feet across this section (Pitzer 1972) . 

The magnitude of the horizontal movement in- 
creased downslope from the flood control channel to 
the lake. For example, at the west fence of the con- 
verter station, the maximum offset was 2.4 feet com- 
pared to 0.7 foot just west of the channel. 

Vertical and horizontal displacements on a section 
across the rupture zone at the Golden State Freeway 
are plotted on figures 4a and 4b, respectively. The 
vertical displacements are the differences between 



plan elevations and postearthquake level data ob- 
tained from the California Division of Highways. 
Secondary vertical displacements were separated 
from tectonic elevation changes across the section as 
follows. South to the rupture zone, the uplift, which 
is assumed to be of tectonic origin, increased almost 
linearly with distance southward. At San Fernando 
Road, north of the rupture zone, the tectonic uplift 
was about 0.8 foot (based on BM 1273 rather than 
SYL BUB, whose stability is questionable) . The rel- 
ative uplift at San Fernando Road is consistent with 
a linear extrapolation of the data south of the rup- 
ture zone. Therefore, it is assumed that the linear 



202 



San Fernando Earthquake of 107I 



1,000 FEET 
_i I 






MAP SCALE 



POL 



JENSEN 



Van Gogh 
School 




I \ PLANT 





FILTRATION * 



EX PL ANATlON 
Vector : 



Offset : 

Surfcce rapture 

5 Feet 



SYL A 12 A 



DISPLACEMENT SCALE 



Figure 3. — Rupture zone west of Van Norman Lake, with horizontal displacements superimposed. 



extrapolation on figure 4a represents tectonic eleva- 
tion change and that deviations from this line are 
the result of secondary effects. 

Based on the above assumption, differential sub- 
sidence as great as 0.5 foot occurred across the rup- 
ture zone. Immediately north of the zone, an anoma- 
lous rise of 0.2 foot was measured; and from there to 
the bridge over San Fernando Road, subsidence up 
to 0.5 foot occurred. A bridge-approach fill underlies 
the latter section of freeway, and the subsidence 
there most likely resulted from compaction of the 
fill. 



On the west side of the lake (fig. 3) , horizontal 
displacement increased with distance downslope. 
The maximum secondary displacement at Balboa 
Boulevard was about 0.8 foot. At the north-south 
axis of the filtration plant, the maximum displace- 
ment was 1.8 feet; and at SYL A12B, the displace- 
ment was about 3 feet. The margins of the displace- 
ment zone corresponded to the margins of the 
rupture zone. 

Points along the north-south axis of the filtration 
plant were releveled periodically by MW'D after the 
earthquake. Elevation changes recorded on February 






Ground Movements in Van Norman Lake Vicinity 



203 



+ 2 




Highway fill 



Bridge 



Rupture zone 



Highway stations 








South 

« 


U"> 

in 

m 


















o 

iX> 
un 






1565 


P| North 

in 


6.0 


(b) Secondary horizontal 






displacements , 














4.0 




















. 


250 


o 

500 FEET a 

i F_ 












Ll_ 


2.0 


























« Nails not set on highway stations 


C 

a 

CO 
































n 


.ft 


i 


















l 




m this section 


i 



Figure 4. 



-Vertical (a) and horizontal (b) displacements along Golden State Freeway at latitude of the rupture zone. 
Elevation data from California Division of Highways. 



10, 16, and 27 (1, 7, and 18 days after the earth- 
quake, respectively) are plotted in figure 5a. These 
changes are with respect to station 8 + 00 north 
which was held fixed (see fig. 3 for location) . Hori- 
zontal offsets at the corresponding stations, relative 
to points on the upland hills (Saugus Formation) at 
either end of the axis, are plotted in figure 5b. Sub- 
sidence occurred across the main rupture zone; the 
maximum was about 0.4 foot. To the north of the 
main zone, both uplift and subsidence were re- 
corded. It is also interesting to note that additional 
relative elevation changes (both positive and nega- 
tive) occurred at many points after the earthquake. 
Similarly, minor horizontal movements occurred 
after the main earthquake; these movements were 
generally downslope, but some upslope movements 
also were recorded. No attempt was made to estimate 
the influence of local tectonic movements on these 
data. 

SUBSURFACE CONDITIONS 

It was beyond the scope of this study to perform 
postearthquake subsurface investigations; work has 



been done by others (Fallgren and Smith 1971; Fall- 
gren and Smith, "Ground Displacement at San Fer- 
nando Valley Juvenile Hall During San Fernando 
Earthquake" in Volume III; and MWD, "Geology, 
Earthquake Damage, and Water Table Fluctuations 
— Metropolitan Water District Facilities, Sylmar 
Area" in Volume III) . Within and along the north 
boundary of the displacement zone northeast of the 
lake, Fallgren and Smith (1971) report the following: 

The soils were dense to medium dense and dry near the 
ground surface. However, soil consistency (firmness) gen- 
erally decreased with depth until a 5- to 15-foot-thick zone 
of saturated and soft, or loose, soils was encountered at 
depths of 10 to 25 feet. Soils in the soft or loose zone con- 
sisted of sandy silt or uniform fine sand. Below the soft 
zone, soil consistency increased and varied from medium 
dense to dense. 

Outside the rupture zone, the soft, saturated soils 
were absent or the soil was of firmer consistency. 
Fallgren and Smith (1971) concluded that slippage 
occurred within the soft, saturated layer, most likely 
as a discontinuous deformation of the layer rather 
than along a single continuous failure surface. 



204 



San Fernando Earthquake of 1971 



+050 









-0.50 



I 



-l.00 L 



(a) Profili 




Feb. 10, 1971 
Feb. 16, 197 
Feb.27,1971 



500 
j i i 



1000 FEET 
i 



South <- 



Stations 



North 



CO 


co 


to 


CO 


</> 


CO 


CO 


CO 


CO 


CO 


CO 


CO 


n 


O 


o 


in 


o 


o 


o 


— 


o 


o 


o 


8 


o 


O 


o 


o 


o 


o 


o 


to 


o 


o 


o 


+ 


+ 


+ 


■¥ 


♦ 


+ 


-t- 


+ 


+ 


+ 


•f 


♦ 


1- 


CM 


o 


CO 


(0 


<t 


CM 


o 


CO 


CO 


^- 


CVJ 


C\J 


CVJ 


CM 


— 


— 




— 













z 


z 


z 


z 


o 


o 


o 


o 


o 


o 


o 


o 


♦ 


+ 


♦ 


♦ 


OJ 


<r 


CO 


•1 



5= 






-m ®- 



Y f T — T — — t — "*" "*" 



~"t"r 



_(b)pi 



an view 



^ 2.0 L 



Figure 5. — Vertical (n) and horizontal (b) displacements along north-south axis of Joseph Jensen Filtration Plant. 
Data from Metropolitan Water District of Southern California. 



Precarthquake subsurface investigations were con- 
ducted at the Juvenile Hall by LeRoy Crandall 8: 
Associates (1961) and at the Sylmar Converter Sta- 
tion by Converse Foundation Engineers (1966) . 
These reports show the soft layer of silts and sands 
identified by Fallgren and Smith (1971). Preearth- 
quake densities measured in this layer ranged from 
80 to 110 pcf. Of particular interest to this study 
were two borings along the east boundary of the con- 
verter station property near the disrupted flood con- 
trol channel. In each boring, a soft, wet, or saturated 
layer of silt or sandy silt was found at depths of 9 
and 1 1 feet, respectively. The depth of the channel 
in this area is about 8 feet, but was excavated to at 
least a 10-foot depth during construction. It is also of 



interest to note that during both the original con- 
struction and the postearthquake repairs to the chan- 
nel, work was hampered by high ground water and 
soft, saturated soils (Pitzer 1972) . 

A brief summary of soil conditions beneath the Jo- 
seph Jensen Filtration Plant, west of the lake, has 
been given in a paper by MWD, "Geologv. Earth- 
quake Damage, and Water Table Fluctuations — 
Metropolitan Water District Facilities. Sylmar Area" 
in Volume III. They report that a saturated laver of 
fine sand was found in several postearthquake bor- 
ings at depths ranging from 6 to 9 feet below the 
original ground surface. Thev infer that slippage 
occurred within this layer, possibly because of lique- 
faction. 



Ground Movements in Van Norman Lake Vicinity 



205 



ORIGIN OF RUPTURE ZONES 

The survey data show that, although the earth's 
crust was uplifted, tilted, and horizontally displaced 
beneath the Van Norman Lake area, differential dis- 
placements outside the rupture zones were small 
compared with differential displacements within the 
zones. If the differential displacements outside the 
rupture zones are a reflection of tectonic movements 
in the underlying bedrock, as is generally accepted, 
then it would be mechanically impossible for the 
larger and, in many instances, oppositely directed 
displacements within the rupture zones to be also of 
tectonic origin; thus, they must be surficial move- 
ments of secondary origin — that is, in some way the 
result of seismic shaking. 

The evidence indicates that landslides, predomi- 
nantly of the lateral spreading type (Varnes 1958) , 
with some rotational slumping on the steeper slopes 
near the shore of the lake, were the causes of the 
rupturing and displacements. Even though the lat- 
eral spreading slides were not as well developed as 
some failures reported in the literature, they meet 
the criteria for this type of failure. 

Northeast of the lake, evidence of lateral spreading 
includes: (1) The feature is tongue-shaped in plan, 
with right-lateral displacements across the northwest 
margin, left-lateral displacements across the southeast 
margin, and extensional displacements at the upper 
margin. (2) Displacements were downslope, with 
maximum horizontal components being several times 
larger than the corresponding vertical components. 
(The latter factor cannot be accommodated by sim- 
ple compaction of subsurface sediments, an explana- 
tion suggested by Scott 1971.) (3) The surface layer 
fractured into large-sized blocks, particularly that 
area north of San Fernando Road. These blocks 
moved downslope with very little tilting, a mode 
characteristic of lateral spreading (Varnes 1958) . 
(4) The soil profile beneath the rupture zone con- 
sists of a firm surface layer overlying a soft saturated 
layer, which is in turn underlain by firm soils to 
depth. This profile is consistent with the three-layer 
profile given by Varnes (1958) for lateral spreading 
failures. 

Several objections have been raised against calling 
the rupture zone northeast of the lake a landslide. 
Scott (1971) noted that if it were a landslide the 
greatest displacements should have occurred at the 
unrestrained face along the lake margin and should 



have diminished with distance to the northeast. A re- 
lated objection is the absence of a sizable landslide 
toe in the lake bottom (paper by MWD, "Geology, 
Earthquake Damage, and Water Table Fluctuations 
— Metropolitan Water District Facilities, Sylmar 
Area" in Volume III) . Both variances from normal 
landslide behavior are explained by survey data that 
show that the flood control channel east of the con- 
verter station acted as a free face or toe. Essentially, 
all of the displacement from upslope was absorbed 
at that point. Thus, the slide can be divided into two 
segments, one extending from the lake to the flood 
control channel and the other extending from the 
channel to the upper margin of the rupture zone. 
Over both of these segments, displacement generally 
decreased upslope. 

Fallgren and Smith (1971) objected to calling the 
feature a slide because relative movement apparently 
occurred across a zone of considerable thickness 
rather than along a single, continuous failure surface 
and because the feature is stable under static condi- 
tions. The first of these objections is eliminated by 
the definition of lateral spreading (Varnes 1958) 
that allows for a thick mobile zone. Indeed, if the 
failure zone had been along a thin layer, the slide 
would have been more properly classified as a block- 
glide. With respect to the second objection, slides 
that are mobile only during periods of seismic shak- 
ing have long been recognized in what would other- 
wise be considered stable ground. 

The rupture and displacement patterns on the 
west side of the lake were more typical of normal 
landslide behavior. The magnitude of the displace- 
ments decreased with distance upslope from the lake, 
and the surface layer was ruptured along lines more 
or less perpendicular to the direction of movement. 
The blocks between ruptures generally moved later- 
ally downslope; however, some blocks rotated 
slightly. Again, it is concluded that the origins of 
these ruptures and displacements were low-angle 
landslides, predominantly of the lateral spreading or 
possibly blockglide types, with rotational slumping 
at the free face near the shore of the lake. 

ACKNOWLEDGMENTS 

Many of the data used in this study were supplied 
by other agencies. Their cooperation and the assist- 
ance of their staff members are gratefully acknowl- 
edged: A. G. Keene and R. J. Mitchell, Los Angeles 



200 



San Fernando Earthquake of 1971 



County Engineer's Office; I. E, Sh inkle, Log Angeles 
Flood Control District; \V. V Meslou and L. I). 
Paulsen, Los Angeles City Bureau ol Engineering I 
|. Vadasz and C. P. Pistole, Los Angeles Department 
of Watei and Power; E. A. Varon, California I)i\i 
sion of Highways; W. ). Edwards, Metropolitan 
Water Districl ol Southern California; and R. B. 
Fallgren and J. L. Smith. FUGRO, Inc. 

REFERENCES 

Clark, MM., U.S. Geological Survey, Menlo Park, Calif., 1971 
(personal communication) . 

Converse Foundation Engineers, Pasadena, Calif., "Foundation 
Investigation, Proposed Sylmai Convertei Station, City ol 
Los Angeles, California," foi the Bechtel Corporation, 
Vernon, Calif., ()<t. 21, 1966, II pp. and 31 figs, (unpub 
lished report) . 

Crandall, LeRoy, "Opinions on Foundation Behavioi During 
San Fernando Earthquake, Exhibit C," Report on Olive 
View Hospital, Structural Engineers Association ol Southern 
California, Los Angeles, Way 25, 1971, 2 pp. 

Crandall, LeRoy, & Associates, Los Angeles, Calif., "Report 
of Foundation Investigation, Proposed San Fernando Branch 
Juvenile Hall, San Fernando Road and Yarnell Street Los 
Angeles," for County of Los Angeles, Calif., Sept. 27, 1961, 
10 pp. and 26 figs, (unpublished report) . 

Duke, C. Martin, "Damage to Water Supply Systems," The 
San Fernando, California, Earthquake of February 9, 1971 
Geological Survey Professional Paper 733. U.S. Geologica 
Survey and the National Oceanic and Atmospheric Adminis 
tration, U.S. Department of the Interior and U.S. Depart 
ment of Commerce. Washington, D.C., 1971, pp. 225-210 

Fallgren, Richard B., and Smith, Jay L., "Geologic and Soil 
Investigation, San Fernando Valley Juvenile Hall, Sylmar 
California," for the Los Angeles County Engineer by 
FUGRO, Inc., Long Beach, Calif., Sept. 20, 1971, 15 pp 
and 2 pi. (unpublished report) . 

Merifield, P.M., "Geology of a Portion of the Southwestern 
San Gabriel Mountains, San Fernando and Oat Mountain 
Quadrangles, Los Angeles County. California." M.A. thesis. 
University of California, Los Angeles, 1958, 61 pp. 



Aforan D.F "Damage to Energy and < 

ti ins " '/ /"" Sun I ii mi mil, ' I 

in, '> . 1971 Geological Survey Professional Papei 733 I S 
Geological Sunn and the National Oceanic ai 
pherii Administration is Department ol ti 
is Department ol Commerce, Washington, DC 1971, 
pp 245 250. 

Pit/' i \ (, Lot Angela Department ol Wat 
Los Angeles, Calif. I'*72 (written communi 

Sen R I "Preliminary Soil Engineering R< ;•■ 
'// the San do Earthq 

1971, Earthquake I irch Laborato 

EERL 71 02 California Institute ol rethnology Pasa 
June 1971, pp. 299 531. 

Slosson. |. ones I . "Engineering GeoU 
nando Valley fuvenile Hall, Exhibit D Report on Olives 
View Hospital, Structural Engineers Association ol Sou 
California, Los Angeles, May 25 1971, 4 pp. 

Thompson, fame* H., "Damage to the Los Angeles County! 
fuvenile Facilities. Sylmar," The San Fernando, CalifornfaM 
l rthquake of February 9, 1971, Geological 
fional Paper 7V) IS Geologica] Survey and the 
Oceanic and Atmospheric Administration, U.S. Depart 
ol the Interior and l.S. Department of Commerce, W'ashJ 
ington, D.C., 1971. pp. 191-102. 

Varnes, D.J., "Landslide types and Pr< Landslide* 

and Engineering Practice H tarch Board Spf-ciaa 

Report 29. Washington. IX 1958, pp. 20-47. 

Youd, I . Leslie, "Landsliding in the Vicinity of the Van Nor-I 
man Lakes" / //. San Fernando, California, Earthqua 
February '>. 1971, Geological Survey Professional Paper 733 J 
I s. Geologic. il Survey and the National Oceanic at 
mosphciic Administration, IS. Department of the Interioij 
and l.S. Department of Commerce, Washington. D.C.. 1971 j 
pp. 105-109. 

Youd, T. Leslie-, and Olsen, H.W.. "Damage to Constructed! 
Works. Associated With Soil Movements and Foundatior 
Failures." The Sati Fernando, California, Earthquake 0\ 
February 9, 1971, Geological Survey Professional Paper 73! 
U.S. Geological Survey and the National Oceanic and 
mospheric Administration. L.S. Department of the Interic 
and U.S. Department of Commerce, Washington, D.C., 1971 1 
pp. 126-132. 



Earth Rupture and Structural Damage 

by San Fernando Earthquake 

in North Sylmar Housing Development 



CONTENTS 


Page 




207 


Introduction 


207 


Scope of Investigation 


208 


Geologic Setting 


208 


Seismic Setting 


208 


Results of Investigation 


208 


Active Faulting 


208 


Damage to Construction From 




Groimd Rupture 


208 


Damage to Fills 


211 


Damage to Houses Not Associated 




With Ground Failure 


212 


Conclusions 


212 


References 



Published with permission of PBS Corporation. 



DONALD O. ASQUITH 

Envicom Corp. 
Encino, Calif. 

F. BEACH LEIGHTON 

F. Beach Leighton & Associates 
Engineering Geologists 
La Habra, Calif. 



INTRODUCTION 

This report summarizes the results of an investiga- 
tion of the geological aspects of earthquake damage 
in a housing development in northern Sylmar. This 
was one of the areas hardest hit by the San Fernando 
earthquake of February 9, 1971. This investigation 
was undertaken at the request of the developer and 
included both developed and undeveloped properties 
in the damaged area. 

The results of the investigation are significant to 
the overall problem of earthquake hazard because of 
the wide range of engineering geologic conditions in 
the housing development including movement along 
an active fault, structures in various stages of con- 
struction, and earth foundation materials, ranging 
from firm bedrock, to moderately firm to soft terrace 
gravels, to manmade fill. Also, geologic conditions in 
the development bear on the evaluation of condi- 
tions and events at the Veterans Administration 
Hospital, located immediately northwest of the de- 
velopment. 

Scope of Investigation 

The investigation consisted of two phases: first a 
surface mapping phase, followed by a subsurface ex- 
ploration phase. The surface phase included mapping 
of geologic units and structure at a scale of 1 inch 
equals 60 feet (1:720) , with emphasis on the line of 
recent fault movement and on cracks and ruptures of 
the ground and structures. The boundary between 
cut and fill areas was determined from maps of to- 
pography and designed grades and was modified as 
necessary in the field. 

The subsurface exploration phase consisted of 
backhoe pits and borings located on the basis of the 
surface investigation. Pits were placed transverse to 



207 



208 



San /■/■inn nd '<> Earthquake of 1 97 J 



faults .md cracks in ordei thai three-dimensional re ings ted during the im 

lationships could be viewed and mapped. marized in table 1. 



Geologic Setting 

The area ol investigation is located at the base "I 
the San Gabriel Mountains (fig. I) in an area ol sed- 
imentary rocks and alluvia] sediments defined by 
Oakeshoti (1958) as Plio-Pleistocene Saugus Forma- 
tion, late Pleistocene terrace gravels, and Recent al- 
luvium. The Saugus Formation in the area is com- 
posed ol brown-to-light-brown sand) siltstone, with 
approximately 25-perceni interbedded aikosie sand- 
stone and pebbly arkose. It is medium to thin bedded 
and well indurated. The terrace gravels consist ol 
granitic detritus, with cobbles and boulders to 2 feet 
in diameter in a matrix ol pebbly, coarse sands. It is 
poorly sorted and moderately indurated. 

The principal structural features in the area an 
the Hospital fault and the Little Tujunga syncline 
(fig. 1). Roe ks ol the Saugus Formation stiikc N v| » 
to 90°E. and dip northward toward the axis of the 
sync line at angles of 60° to 80°. The terrace gravels 
unconformably overlie the Saugus Formation and 
are relatively flat. 

Seismic Setting 

The area of investigation is located approximately 
1.5 miles north of the Sylmar segment of the San 
Fernando fault zone and 5 miles south of the epicen- 
ter of the February 9, 1971, earthquake. Maximum 
ground accelerations ol ()..") to 0.75g, with high-fre- 
quency peaks to l.Og (Maley and Cloud 1971) . were 
recorded at Pacoima Dam approximately 0.9 mile to 
the northeast. 

RESULTS OF INVESTIGATION 

Active Faulting 

An active fault extends diagonally across the hous- 
ing development (fig. 2) . This fault has been named 
the Veterans fault because of its close proximitv to 
the Veterans Administration Hospital. However, it 
should be emphasized that it has not been possible to 
trace the fault westward to the grounds of the hos- 
pital and that a westward extension of its trend does 
not pass through or near the hospital wing that 
collapsed in the earthquake (fig. 2) . 

The principal characteristics of the fault, as ex- 
posed on lot pads, in cut slopes between pads (figs. 3 
and 4) , in backhoe trenches (e.g., fig. 5) , and bor- 



I). image to Construction From GffDUSld Rupture 

I he Veterans fault had not been r< 
the development be-loie- the earthquake oi d 

the time homebuilding was in j fortur, 

only one- house had been built ovei the- trace of the 
fault, and it was not occupied at the time of the 
earthquake. Thai house and the two adjacent h 
were still undei construction, but were complete 
the extent that stucco had been applied to the outer 
walls and eh \ wall to the- inside. Damage to the house 
on the- trace ol the fault included rupture and offset 
ol the garage-floor slab overlying the fault, tiltii 
the house slab, and severe clacking of the walls in 
the raised not thwe-st-e orner bedroom. While the 
house was a total loss because of the foundation dam- 
age, the limited extent of the damage to the upper 
paits of the structure indicates that se\ere injury 
probably would not have cKcurred had the house 
been oc e upied. 

Damage to the two adjacent houses was limited to 
minor c tacking between footings and floor slabs and 
to sour- small cracks at the joints between sheets of 
drywall. The house to the west is approximately 5 
feet from the fault, and the house to the east is ap 
proximately 10 feet from the fault. 

Damage to Fills 

The most significant damage in the housing devel- 
opment was related to settlements at the boundary 
between natural and fill materials and to failures of 
fill slopes. 

The largest failure of a fill occurred at the north- 
east corner of the development (near B' on fu 
Here fill was placed on a northeast- to east-facing 
slope composed of Saugus Formation, with alluvial 
sand at the toe (northeast end of cross section B-B', 
fig. 4). Vertical settlement at the cut-fill boundary 

Table I.— Principal characteristics of Veterans fault 

Trend N\80 = to 85 C E. turning to N.60 = E. near its 

westernmost exposure. 

Dip 60 = to 70~N. (approximately parallel to 

bedding in Saugus Formation I, decreasing 
to 35 = to 40° at west end. 
Movement (February 6 to 8 in., decreasing to 2 to 3 in. near loca- 
9, 1971). tion where fault is beneath fill at east and 

west end of exposure. 
Movement (pre- 7f) ft (fig. 6). 

1971). 
Formations faulted .. . Saugus Formation 'Plio-Pleistocene and 

terrace gravel (late Pleistocene). 
Width of rupture ' o to 2 in. 

zone. 



Earth Rupture and Structural Damage 



209 






% mm, 









Epicenter of 

February 9. 1971 

earthquake 



! 






£SS ;%/ 



LEGEND 

Qal — Alluvium Recent" 

Qt — Terrace deposits (Late Pleistocene") 

OT — Sediments Tertian.- and Quaternary 

Fault 

Fault alon? which displacement 

occurred February 9. 1971 



• . ■ 



'"■■'- 1 



I 



--- - .- 

ti ' 

^ V: 

Qt ^- A. /I ^ ~ 







Figure 1.— Geologic index map. 



210 San Fernando Earthquake of 1971 



200 4(10 


HOI 




l] 'i 





i, v. (.; k n n 

Qt Terrace de] 

Ta S;tunua f"i mal Lon 

J? Veteran's fault 

*r Cut-fill boundai | 



Assignment of geologic units 
after Oakeahotl (1958) 




Figure 2. — Geologic map of housing development. 

was approximately 12 inches, and the slope at the uted to settlement ol the alluvial sand at the toe of 

boundary ranges from approximately 1.5 to 1 to 2 to the slope. Settlement of alluvial sand and gravel was 

1. A downslope movement of 18 to 24 inches is indi- common in the canyons in the area. No houses had 

cated. The large magnitude of this failure is attrib- been built on the lots in this part of the develop- 




Figure 3. — Cross section A-A'. 






Earth Rupture and Structural Damage 211 



Topogrophy 
prior to grodmtj 



J9U^ 



1440- ' 



Figure 4. — Cross section B-B'. 

ment, and damage was limited to rupture of streets, 
sidewalks, and utility lines. 

Settlement of the fill in the central part of the de- 
velopment (near A and B of cross sections A-A' and 
B-B', figs. 3 and 4) was much less severe. Tension 
cracking and settlement in the range of 1 to 3 inches 
were common along the cut-fill boundary and near 
the base of some fill slopes. Damage to houses built 



on the fill was generally moderate, but was locally se- 
vere where one house had been built over or near 
the boundary between cut and fill. 

In addition to general cracking along the cut-fill 
boundary, failures occurred at the corners of some 
fill embankments. These failures were particularly 
severe where heavy watering of lawns and shrubbery 
had preceded the earthquake. Much of the heavy 
damage to the model homes, watered regularly each 
night by an electrically timed sprinkling system, can 
be attributed to excessive moisture content of the 
soil. Extensive failures of embankments as low as 2 
to 3 feet in height occurred between some of the 
models. 

Damage to Houses Not Associated With Ground 
Failure 

Incomplete houses, all of similar construction, sus- 
tained some of the most spectacular damage in the 
development. All were located on Saugus Formation 
or terrace gravel and were of one-story frame and 
stucco construction, with trussed roofs and slab 
floors. The extent of damage followed a regular pat- 



riate :i-ig-71 



ATTITUDES 



ENGINEERING GEOLOGY DESCRIPTION 



PHYSICAL 
CONDITION 



COMMENTS 



Bedding 
©N75W, 63N 

N50W, 66N 

©N85W, 55N 

Fault 
)N85E, 61N 

Cut-fill 
©N45W, 29NE 



Gv, Terrace gravel with pebbles and cobbles to 8" principally of weathered granite 

rocks in matrix of coarse sand, silty. 

Sit + Cstn, Siltstone, red-brown with 10-20% claystone, red-brown, medium plastic 

Ss, Sandstone, light gray, medium to fine grain, arkosic 



Slightly damp, 

soft 

Slightly damp 

to dry, firm 

Slightly damp 

to dry, mediun 

firm 



Saugus im 



NATURAL 
SLOPE 



Flat 

(on graded 

lot pad) 



GRAPHIC REPRESENTATION 



Pittrend= N27E 




Figure 5. — Geologic pit log No. 2. 



212 San Fernando Earthquake <>f 1971 



c 



- 



- 







Figure 6. — Cross section C—C'. 

tern. Many of the houses that had been framed and 
roofed, but which were without either interior or ex- 
terior walls, collapsed. The trussed roofs remained 
essentially intact, but the wall frames failed as a re- 
sult of breaking of the diagonal bracing and the 
studs. The houses that had been papered and wind 
for stucco failed in a similar manner, but did not 
collapse completely. The wire held them in leaning 
positions at angles of approximately 30 from the 
vertical. The houses that had been stuccoed on the 
outside and had (he drywall installed on the inside 
sustained very little damage. 

Damage to completed houses was similar to the 
damage to houses in other parts of Sylmar and San 
Fernando. Two weak points stand out: the un- 
braced door-wall of the garage and the independent 
construction of the two levels of two-story houses. 
Where the upper level of the house was built over 
the garage, the damage was often particularly severe. 

CONCLUSIONS 

1 The housing development was subjected to 
ground rupture of up to 8 inches vertically along the 



active Veterans fault and to ground shaking 
maximum a< < derations of at least 0.5g. 

2 'I lie one house built over the trace of the 
erans lault in bedrock was damaged beyond repair, 
but the two adjacent houses, also on bed km 
cated approximately 5 and 10 feet from the tr;: 
the fault, were essentially undamaged. Apparently, 
setback fiom active or potentially active fault i 
loi normal residential construction need not he 
where the /one of movement is narrow and the 
amount ol antii ipated display ement is small. 

'. Fills located ovei the active Veterans fault 
were not cut by the fault, but moved as independ- 
ent, cohesive units. Consequently, dam.: much 
more extensive in areas of fill and along the cut-fill 
boundary than in areas of bedrock. T his su_ 
that houses should not be constructed on any part of 
a cohesive fill placed over an active- or potentially ac- 
tive- fault, and that reexamination ol grading and 
construction procedures along the cut-fill boundary 
in seismically prone areas is needed. 

4 Sidehill fills, toed into alluvial sand, settled by 
abnormally large amounts because of compaction of 
the sand eluiino ground shaking. The compaction 
characteristics of some natural materials (e.g., loose 
alluvia] sand) under conditions of seismic shaking 
need additional attention of the soils engineer. 

REFERENCES 

Maley, R.P.. and Cloud, W.K.. "Preliminary Strong-Motion 
Results From the San Fernando Earthquake of February 9, 
1971." The San Fernando, California. Earthquake of Febru- 
ary 9, 1"7I . Geological Survey Professional Paper 733. U.S. 
Geological Survey and the National Oceanic and Atmos- 
pheric Administration, U.S. Department of the Interior and 
U.S. Department of Commerce, Washington, D.C., 1971, 
pp. 163-176. 

Oakeshott. Gordon B.. "Geology and Mineral Deposits of San 
Fernando Quadrangle. Los Angeles Countv. California," 
California Division of Mines Bulletin 172, Feb. 1958, 147 pp. 



Geology, Earthquake Damage, 
and Water Table Fluctuations — 
Metropolitan Water District 
Facilities, Sylmar Area 



CONTENTS 

Page 

213 Introduction 

214 Survey Data 

214 Damage to Balboa Inlet Tunnel 
214 Movement of San Fernando Tunnel 

214 North Olive View Fault 

215 Juvenile Hall Landslide 

217 Movement at Joseph Jensen 

Filtration Plant 

218 Pattern of Cracks and Relation to 

Damage 
220 Fluctuations of Ground-Water 

Levels 
222 References 

From material provided by Richard J. Proctor 
and William J. Edwards. 



METROPOLITAN WATER DISTRICT 
OF SOUTHERN CALIFORNIA 

Engineering Geology and Survey Branches 
Los Angeles, Calif. 



INTRODUCTION 

The Metropolitan Water District of Southern Cal- 
ifornia (MWD) is involved in major construction in 
the Sylmar-San Fernando area for the distribution 
system for State Project ("Feather River") water. 
This construction involves large-diameter tunnels, 
pipelines, and a 400-million-gallon-per-day-capacity 
water treatment plant located at the northwest end 
of upper San Fernando Valley. 

The Engineering Geology Branch of MWD has 
been investigating this area for tunnel routes since 
1962 (Proctor et al. 1966) . Geologic maps prepared 
by MWD were provided to all interested governmen- 
tal and private agencies some years before and were 
furnished immediately after the February 9, 1971, 
earthquake. These maps relate to the San Fernando 
Tunnel (now under construction) and the two Sun- 
land Tunnels (now in the proposal stage) . Preearth- 
quake knowledge of the geology and faults in this 
area was surprisingly complete, but much of the in- 
formation was in the form of in-house reports and 
maps (fig. 1) . Most faults, along which movement 
took place, were known previously; but some of 
these were not the faults that appear on published 
maps. 

A program of 54 test borings was initiated to ex- 
amine subsurface lithology and to locate faults along 
proposed tunnel alignments. Cores of fault zone ma- 
terials were studied in detail, and perforated casing 
was installed in many borings to obtain hydrologic 
data. Results from programs of investigation were re- 
ported on geologic maps and in descriptions of condi- 
tions, including potential hazards pertinent to tun- 
neling in the area. Among the most important 



213 



214 San Fernando Earthquake of 1971 

engineering considerations were faults that could be 
intersected during tunneling. These faults were stud- 
ied to define position, thickness of /ones of crushed 
rock and gouge, amount of displacement, and when 
movement occurred. 

SURVEY DATA 

Preliminary route surveying for State Project 
water distribution lines began in the early 1960s 
and, fortunately, involved establishing bench marks 
and triangulation points. The surveys taken in the 
weeks after the major shock provided precise meas- 
urements of ground distortion in many localities. 
These surveys are discussed under the sections on in- 
dividual MWD facilities that were damaged. 

The maximum measurement of ground displace- 
ment from recent MWD trilateration surveys was 2.5 
m. This appears as shortening between north-south 
oriented points 6.6 km apart (Pacoima-2 on the hill 
west of Hansen Dam, south of the known surface 
breaks; Washington— 2 on Sugarloaf Peak in upper 
Lopez Canyon, east of fig. 1). Washington-2 moved 
westward and southward, as did most points north of 
the surface ruptures, and also moved upward 1.3 m, 
as averaged between U.S. Geological Survey (USGS) 
elevation stations (USGS and NOAA 1971, p. 82, 
figs. 1 and 2) on either side of Sugarloaf Peak. The 
MWD trilateration was by electrotape on a network 
previously surveyed in 1969. 

DAMAGE TO BALBOA INLET TUNNEL 

In the 1-mile-long Balboa Inlet Tunnel, the zone 
of damage occurred in an area 26 m long that is ap- 
proximately 46 m south of the lower branch of the 
Santa Susana fault, as mapped during tunnel excava- 
tion. The damage to the tunnel consisted of severe 
spalling and breaking of the concrete lining and of 
deformation of the reinforcing steel bars (figs. 2 and 
3) . The zone of damage occurs in an area where the 
tunnel lies below a canyon. The damage itself is lon- 
gitudinal in relation to the tunnel alignment, and, 
hence, it is not parallel to bedding or mapped fault 
traces. Because of this relation and the discordance 
in location of the damage relative to the mapped 
fault, we believe that the zone of damage is a result 

7 o 

of strong ground shaking in the tunnel under local 
shallow cover. A resurvey of the Balboa Inlet Tun- 
nel showed that the invert at the south portal rose 8 



cm relative to that in the damaged .. ■ - • 1 lie tuiufl 

remains on grade north ol the damaged a 

Some surface craefs appear along the upper 
branch ol the Santa Susana fault in an area 460 m 
north of the intersection of the lower branch win 
the Balboa Inlet Tunnel. As much as II rrn of left- 
lateral displacement occurred across the Golden State 
way and foothill Boulevard, but dama^< to the 
tunnel lining was not observed directly \>< 
these ( ra( ks. 

MOVEMENT OF SAN FERNANDO II WFL 

The cumulative total vertical displacement result- 
ing horn the earthquake is at least 2.3 m, as mea- 
sured along the 9-km-long San Fernando Tunnel. 
The east portal of this pressure tunnel is just north 
of the Sylmar fault, and it will terminate in the west 
at a 48-foot-diameter (about 15-m) construction 
shah located in Magazine Canyon (fig. 1). Survey 
leveling extending eastward from the shaft has 
shown a 1-foot ground rise from the shaft to a point 
west of the large bend in alignment near the middle 
of the tunnel. From this bend to the east portal, the 
survey indicates a gradual rise in tunnel elevation to 
the maximum of 2.3 m. The absence of recognizable 
shear surfaces in the tunnel is consonant with re- 
ports from miners present in the tunnel at the time 
of the earthquake. The miners were excavating with 
a 22-foot-diameter (6.7-m) mechanical boring ma- 
chine at the working heading, then 6 km in from the 
east portal. The material at the face was soft, water- 
saturated silt, sand, and gravel (old alluvium) . The 
earthquake was accompanied by an outage of electri- 
cal power that caused the water pumps to stop. Amid 
the attendant confusion and anxiety, the miners 
made their way to the locomotive and drove out of 
the tunnel; this means that the rails were not suffi- 
ciently distorted to cause a derailment. 

NORTH OLIVE VIEW FAULT 

During exploratory drilling for the San Fernando 
Tunnel in 1965, anomalous water levels were ob- 
served between auger borings A-3 and A-4 along 
Foothill Boulevard near the intersection of Glenoaks 
Boulevard (fig. 1) . Measurements in these and other 
nearby borings showed water-level differences (north 
side higher) of more than 21 m. Subsequent ground 
examination in the adjacent foothills disclosed a 



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EXPLANATION 

LANDSLIDE DEPOSITS Majority of slides existed before Feb. 9th earthquake. (Qls in section) 
ALLUVIUM Stream-laid debris of silt, sand and boulders. 

OLD ALLUVIUM Tan, silty sand to coarse conglomerate- soil formation on surface. 

TERRACE DEPOSITS Older alluvial debris at higher levels. 

SAUGUS FORMATION Brown and tan, poorly cemented sandstone and conglomerate, greenish-gray 
sandstone, and reddish-brown siltstone. Mainly non-marine origin. 

SUNSHINE RANCH FORMATION Pale green, mostly soft, sandy siltstone with minor amounts of sand- 
stone and conglomerate. Shallow marine origin. 

PICO FORMATION Yellow-brown, soft to very hard, sandstone and conglomerate, with minor amounts 
of greenish-gray siltstone. Locally, the conglomerate beds are the hardest sedimentary rocks in 
the region. The upper part interf ingers with the SAUGUS FORMATION , the lower part with the 
TOWSLEY FORMATION. Marine origin. 

PICO and/or TOWSLEY FORMATION (S) Mostly light brown and gray sandstone with some 
generally soft siltstone and mudstone", local lenses and beds of conglomerate. Marine origin. 

TOWSLEY FORMATION Brown, mostly soft siltstone and mudstone, light brown and gray sand- 
stone and conglomerate. The upper end interf ingers with the PICO FORMATION. Marine origin. 

BASEMENT COMPLEX Gneiss, quartz diorite, granite. 



SYMBOLS 



^ Xfc CONTACT 

""N. CONGLOMERATE BED or LENS 

FAULT Dashed where approximately located, dotted 
"**» . where conceoled. U'- up -thrown side; D : down- 
thrown side. 

SURFACE FAULTING (2-9-71) Showing dip. U : 
up-thrown side; D : down-thrown side, arrows 
indicate relative movement. 



SURFACE CRACKS and SECONDARY SHEARS (2-9-71) 
^s^^^ U : up-thrown side; D : down-thrown side, arrows 

— * "** indicate relative movement. 



\. 



AXIS OF ANTICLINE Dashed where approximately 
located, dotted where concealed or interred. 



AXIS OF SYNCLINE Dashed where approximately 
\.. located, dotted where concealed or inferred. 

AXIS OF OVERTURNED SYNCLINE Dashed where 
^.. approximately located, dotted where concealed 
or inferred. 

«r STRIKE AND DIP OF BEDS 
y STRIKE OF VERTICAL BEDS 
70 X STRIKE AND DIP OF OVERTURNED BEDS 

• M.W.D. TEST HOLE 

© TEST HOLE Post-earthquoke 

O WATER WELL 

® M.W.D. EXPLORATORY SHAFT 

-y- ABANDONED EXPLORATORY OIL WELL 




J 



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i ' \ ' 2\ • • • • 



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. HEADING OF TUNNEL AT TIME 
OF FEB. 9, 1971 EARTHQUAKE. 



M.W.D. SAN FERNANDO TUNNEL 



Qt / Uh f-ttf. 9, Wri tAHIHWUAKt. y^ 

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1 1 2 1 1 1 S II S 1 1 SECTION ALONG M.W.D. SAN FERNANDO TUNNEL § grg SANDST0NE g^j s|ltstone ^ 



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SANDSTONE 8 CONGLOMERATE 



GEOLOGY MOSTLY FROM UNPUBLISHED MAP BY RM.MERIFIELDU958), MA. THESIS (U.C.L.A.). 



1000 



T==r 



2000 



METERS 



o 1000 

H H H "ZEE 



2000 



3000 4000 

IE 



5000 6000 

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FEET 



Figure 1. — Geologic map and section along the 5.5-mile San Fernando Tunnel. This drawing is similar to those furnished prospective tunnel contractors by Metropolitan Water District of Southern California. 



Geology, Earthquake Damage, and Water Table Fluctuations 215 







Figure 2. — Balboa Inlet Tunnel earthquake damage com 
mainly of spalled concrete in longitudinal cracks. 




Figure 3. — Balboa Inlet Tunnel earthquake damage 
showing deformed bars. 



fault in bedrock trending toward this ground-water 
barrier in the alluvium (fig. 4) . Differences in 
ground-water levels indicate that this fault extends 
southwestward into the alluvium; this particular 
fault has been named the North Olive View fault by 
MWD geologists. A linear contrast in vegetation 
tone is clearly shown on a 1929 vertical aerial photo- 
graph. This feature strikes N.55°E., coincides with 
the projected fault trace, and extends to the San Fer- 
nando Valley Juvenile Hall. We cannot definitely as- 
sign recent tectonic activity to this fault, but differ- 
ential movement by shaking may have occurred 
along it in February 1971. 



A 3-m-deep postearthquake exploratory trench was 
excavated across the northern boundary crack (strik- 
ing N.52°E.) of the Juvenile Hall landslide. The 
trench revealed dark humus-rich soil, smelling of hy- 
drogen sulfide, which was cut by the crack that was 
nearly vertical; almost 30 cm of vertical displacement 
had occurred. 

A southwestward projection of this crack goes 
through the earthquake-damaged Van Gogh Street 
Elementary School. Partly because the school was 
built on alluvium, the damage and surface cracks 
here were more abundant than on the adjacent 
sandstone bedrock; thus, the cracks cannot definitely 
be attributed to fault movement. However, a dis- 
continuous zone of cracks can be traced for several 
blocks fartber southwest in streets and curbs directly 
overlying the Saugus Formation bedrock. An oil 
exploration map prepared for a major oil company 
shows a buried fault essentially in the same position 
as is shown for the North Olive View fault. 

JUVENILE HALL LANDSLIDE 

An alluvial slide, 1.2 km long on a surface slope of 
only li/9°> occurred through the San Fernando Val- 
ley Juvenile Hall (Los Angeles County-owned facil- 
ity) and Sylmar Converter Station (owned by the Los 
Angeles Department of Water and Power) of the Pa- 
cific Intertie. The slide features included: (1) 
sand boils; (2) movement with south side down 
(maximum 28 cm or 1 1 in.) and right-lateral dis- 
placement along the northern boundary cracks; (3) 
movement with north side down and left-lateral dis- 
placement along the southern boundary cracks; and 
(4) northeast closure of these boundary fractures in 
a zone of tension cracks 90 m wide (Youd 1971). 
The slide moved southwestward at least 1.5 m. The 
following evidence indicates that this feature proba- 
bly resulted from a combination of sliding and set- 
tlement caused by seismic compaction of poorly con- 
solidated alluvium, with the north boundary 
coincident with the North Olive View fault. 

The margins of the slide can be traced southwest- 
ward to the converter station where they become less 
distinct. No typical landslide toe has been observed. 
A large area where a toe could form is in or near 
Upper Van Norman Reservoir. Examination of the 
reservoir (while almost drained) disclosed no toelike 
feature attributable to more than minor bank fail- 
ures. Saturation of alluvium in this area may have 



216 San Fernando Earthquake of 1971 




Bfcita 






SNOUVA313 



Geology, Earthquake Damage, and Water Table Fluctuations 217 



resulted from a rise in water table accompanying res- 
ervoir filling in 1921. However, the water table 
north of the fault (Grapevine Canyon drainage) 
may have been very close to the ground surface. The 
general saturation of the alluvium may well have 
contributed to the local sliding and settlement along 
the fault boundary. 

Fences that mark the east and west property lines 
of the converter station were resurveyed by the Los 
Angeles Department of Water and Power (Dunlap 
1971) with the following results: The central part of 
the eastern fence moved a maximum of 1.5 m west- 
ward in relation to "zero points" at the north and 
south ends of the property. The central part of the 
western fence moved westward only 0.7 m. The east- 
ern fence is adjacent to and east of a drainage canal 
(Youd and Olsen 1971, p. 127), which was severely 
buckled. The canal, therefore, probably absorbed 0.8 
m of the slide movement, with the remainder of the 
toe dissipated around Upper Van Norman Reservoir 
where most of the sand boils occurred. The maxi- 
mum relative subsidence within the converter station 
was 23 cm. 

Northwest-southeast shortening also occurred 
across the slide area, as evidenced by the compression 
of curbs and of the Southern Pacific Railroad tracks 
which cross the slide. The tracks were compressed 
into tight curves both downslope and upslope to the 
direction of sliding (fig. 5) . Tension features and 
bowing of the tracks downslope should have oc- 
curred if only sliding was involved. Lengths of track 




Figure 5.— Southern Pacific Railroad tracks, looking west across 
eastern boundary of Juvenile Hall landslide. Note contortion of 
rails both downslope and upslope to direction of sliding (to the 
left). Rails at left were sheared. 



had to be cut and removed to make the lines straight 
again. 

The depth to water in a postearthquake test hole 
in sandy alluvium south of the Juvenile Hall was 4.3 
m on April 20, 1971. Thus, the conditions are met 
for both seismic consolidation causing subsidence in 
this area and for the low-slope landsliding possibly 
aided by liquefaction. 



MOVEMENT AT JOSEPH JENSEN 
FILTRATION PLANT 

This $25 million water-treatment facility was 
under construction, and portions, such as the fin- 
ished water reservoir, sustained extensive damage 
mainly from severe shaking of wet foundation mate- 
rials (fig. 6) . (See also discussion in Jennings 1971, 
pp. 434-449.) A 100-foot-diameter (30.5-m) , 30-foot- 
high (9-m) steel water tank on sandstone bedrock 
suffered atypical damage (figs. 7 and 8) . Surveys in- 
dicate some uplift and left-lateral movement of the 
plant in relation to an established point on bedrock 



„*». 











Figure 6. — Landslide tension cracks in fill at Joseph Jensen 
Filtration Plant. 



218 



San Fernando Earthquake of 1971 



near the north portal ol the Balboa Outlet Tunnel which underlie* the plant lite, hat been corn: 



at the south end of the plani site. In addition, there 
has been some not th soutli shortening, which indi- 
cates that the Mission Hills (Merrick) syncline, 




Figure 7. — Water tank ill Joseph Jensen Filtration Plant. Tank was 
about one-half full at time of earthquake, and rocking caused 
anchor bolts to be pulled out. Well-trussed roof resisted initial 
accelerations more than upper shell wall. 



I he base or sole of sliding ai the plant and at thj 
[uvenile Hall probably occurred along a liq 
layer caused by seismic shaking of the subsoiU 
n hese an- two separate slides , It was est i man 
Seed (1971) that liquefaction beneath the \ 
Jensen Filtration Plant did not occui until afte 
about 10 seconds of shaking ('major shear-wave dura 
lion was about 12 seconds). Several postearthejuak 
boring! at the plant revealed a saturated fir. ■ 
layer 2 to 3 rn below the original ground surface. 

Two a< < elerorneters were installed for MWD a 
the filtration plant In Converse, I)a\is & Associate 
after the main shock of February 9, one on fill 3 
feet (11 mi tint k and one orr soft sandstone of th 
Saugus Formation. The records of two aftershock 
have interesting implications in relation to seismi. 
design and the acceleration of gravity: 



After short 
date 



3-30-71 
3-31-71. 



After- 
shock 

magni- 
tude 

3.7 
4.9 



Peak ground 
acceleration 

Fill Bedrock 

Q.\2g 0.06g 

O.lOfc 



Distance from 
epicenter 

3.2 miles (5.1 km 
4.5 miles (7 .2 km* 




Figure 8. — Anchor bolt pulled out 13 inches at base of 
Joseph Jensen Filtration Plant water tank. 



PATTERN OF CRACKS AND RELATION 
TO DAMAGE 

Many surficial cracks appeared throughout the Syl- 
mar area during the earthquake. These are nontec- 
tonic and can be attributed to lurching effects, com- 
pression ridges, tension cracks, subsidence, and 
insipient landslides. Cracks representing these fea- 
tures were not significant at MWD facilities, except 
for the landslide cracks at the Joseph Jensen Filtra 
tion Plant. Other significant cracks should be men 
tioned, however, because overlying structures were 
selectively damaged. Some examples follow. 

Surficial cracks at Olive View Hospital (fig. 9), 
which are compressional, cannot be traced very far 
and are nontectonic. Thus, it should be stressed that, 
in our opinion, the spectacular damage to the new 
$27 million Olive View Hospital and damage at the 
Veterans Administration Hospital resulted entirely 
from the effects of ground shaking. That the intensity 
of ground shaking was so great here (Modified Mer- 
calli intensity VIII-XI, Scott 1971, p. 153) should 
not be surprising considering: (1) The Sylmar basin 
is on the upper plate of a thrust-fault wedge; thus, 
the rupturing along the fault planes passed closer to 
the surface over the basin than at the hypocentral 



Geology, Earthquake Damage, and Water Table Fluctuations 219 




Figure 9. — Water tank at Olive View Hospital. The belling at 
bottom of tank occurred during the earthquake by sloshing water, 
causing the tank to rock back and forth and thus "walk" off its 
foundation. Note lack of anchor bolts. 

depth of 12 km. (2) The northern end of San Fer- 
nando Valley is the interface between high-velocity 
crystalline basement rocks and low-velocity alluvium 
and sedimentary rocks. (3) The buried sedimentary- 
granitic interlace or bottom of the basin may also be 
directly beneath the northern end of the valley, be- 
tween the faulting and the epicenter. Housner (1966, 
p. ill— 105) states: "The intensity of ground shaking 
immediately adjacent to a fault is not especially se- 
vere but is, in general, somewhat less than at a dis- 
tance of several miles from the fault." 

Extensive damage to new homes in the tract east 
of Olive View Hospital appears to reflect a lack of 
adequate internal bracing rather than fault lines. 
Most one-story houses in this area withstood shaking 
better than the split-level houses which have the mas- 
ter bedroom over a two-car garage. Such garages have 
a single large door and are without internal cross 
bracing; many of them collapsed (fig. 10) . 



Figure 10. — Typical split-level home with collapsed two-car garage; 
Almetz Street, Sylmar. 



Some types of highway bridges and overpasses dis- 
played unacceptable performance when subjected to 
ground shaking (figs. 11 and 12) . No faults underlie 
the 42 bridges damaged; five suffered complete col- 
apse (Jennings 1971, p. 366) . 

Small but continuous cracks south of Astoria 
Street are associated with selective damage to the Syl- 
mar High School buildings. In two places, sidewalk 
slabs were thrust under the building as much as 4 
inches (10 cm) . One ground crack at the school 
trends toward two compression ridges that buckled 
the newly opened Foothill Freeway (Interstate 210) 
on both sides of the Astoria Street pedestrian cross- 




Figure 11. — Crane was crushed by UO-ft tall column, similar to 
one in background, which sheared near ground surface, causing 
span of bridge to fall on freeway and railroad tracks. Construc- 
tion similar to this design is currently underway for San 
Bernardino -liars tow Freeway interchange in Colton where the 
foundation is adjacent to San Jacinto fault in Santa Ana River 
sand. 



220 



San Fernando Earthquake <>\ 1971 








« AT 




Figure 12. — Collapsed highway overpasses at northwest end of Sylmar arm. 



ing (fig. 13). At one compression ridge, the north 
slab overrode the south one by 18 inches (about 45 
cm) . The freeway pavement was sawed and most 
slabs displayed separation, in places amounting to 
li/2 inches (4 cm), suggesting local extension be- 
tween the compression ridges. North-south compres- 
sion (shortening) is thus well expressed on the free- 
way here and farther south at the Sylmar fault trace 
across and west of the freeway. Total shortening may 
amount to as much as 2.3 m, as revealed by surveys 
of Southern California Edison Company transmis- 
sion tower bases from points north of the valley to 
Hansen Dam (McNey 1971) . 

FLUCTUATIONS OF GROUND-WATER 
LEVELS 

MWD routinely measures the ground-water levels 
in 33 wells and observation holes between Grape- 
vine Canyon in northwest Sylmar and Big Tujunga 
Wash. The purposes of these measurements are to 
predict the limits in which ground water will be 
encountered during tunnel excavation and to have a 
prior record for ground water in the event that tun- 
nel construction may damage water production by 
lowering the water table severely. Most measure- 
ments began in the mid-1960s and are on a monthly 
basis. 



mhmI 

i i 7 


HBP' " <****■• 








Figure 13. — Compression ridges across freeway pavement near 
Astoria Street pedestrian crossing. 



Geology, Earthquake Damage, and Water Table Fluctuations 221 



a 
Q 





OB-8 SF Sylmar 




\ 




















\ 






1 






122 








A 




A 




.. 




2-10-71 






\ 












3:15 






\ 












D/W 122.40 meas. 




\ 










2 


RLB/DHK 






|| 


M=3.0 






3-11-71 










\l 








9:55 










A 






D/W 129. 98 meas. 


.4 












RLB/DHK 


M=3.8 










M=3.3 








.6 


• 








a! 




l\ 




\ 












A 


• 




|M=3.2 


IV 


=3.0 








\ 




.8 
123.0 


A 






1 M=3.0 








I 




\ 




1 A 


A 1 

A 


M=3.4 








i 












\ 






M=3.3 


















A 








2 - 








I 
















h 


' f 


















h 






M= 


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A v 






4 




1 






•\ 


















\ 




/ 


\ 












1 






'1 




^ 


\ 




A | 






6 - 




JJ M 


=3.2 




























A \ 






1 


0,11,1 


2,13 , 


A M=3.4 

15 16|17|l8,19,20,21 


1,1 ,24,25 


26,27,28, 1 


2| 3, 4 | 5 


6 1 7 I 8 | 





February 



March 



Days 



LEGEND: 

M = Earthquake Magnitude 

A = Aftershock (16 in total). Length of line 

associated with A corresponds to length 

of aftershock jiggle on recorder chart. 

gure 14.—Hydrograph of MWD observation hole No. 8 in northwest Sylmar area. At least 16 aftershocks are recorded here because 
their epicenters were close to the recorder; some of the larger magnitude aftershocks, more than a few miles distant, were not 
recorded. 



222 San Fernando Earthquake of 1971 



Most of the wells ;iikI observation holes were meas- 
ured 3 days aliei the earthquake ol February 9; the 
following summarizes the results: The water levels 
in 18 wells (55 percent) dropped, lose in six wells 
(18 percent), and was essentially unchanged in nine 
wells (27 percent) . Most water levels in wells in the 
Sylmar basin rose, while the levels in the foothills 
east of Pacoima Wash dropped. The average < hange 
was of the order of 2 feet (60 (in;. The most dra- 
matic drop occurred in Kagcl Canyon, north of the 
Kagel fault, where the water levels in five wells 
dropped 28, 32, 45, 80, and 100 feet (8.5, 10, 14, 20, 
and 30.5 m) from their preearthquake levels. This 
may residt from dilatancy or expansion of the aqui- 
fers, causing more pore space. Conversely, the rise in 
some wells may be the result of local compression of 
the aquifers. Most wells recovered slowly, but some 
have only partially recovered. 

The earthquake and some aftershocks were perma- 
nently recorded on several local water-level recorders 
and in San Jacinto Valley 90 miles (145 km) south- 
east of the epicenter (fig. 14) . 



REFERENCES 

Albee, A.L., and Smith, , J.L., "Earthquake Characteristics 
and Fault Activity in Southern California," Engineering 
Geology in Southern California, Association of Engineering 
Geologists, Arcadia, Calif., 1966, pp. 9-33. 

Anderson, M.M. (Metropolitan Water District of Southern 
California, Los Angeles) , "Construction of a Two-Million 
Gallon per Day Water Distribution System," paper pre- 
sented at the meeting of the American Society of Civil Engi- 
neers, Memphis, Tenn., Jan. 28, 1970. 

Bonilla, M.G., "Surface Faulting and Related Effects," Earth- 
quake Engineering, Prentice-Hall, Inc., New York, N.Y., 
1970, pp. 47-74. 

Dunlap, John T., Los Angeles Department of Water and 
Power, Los Angeles, Calif., 1971 (personal communication) . 

Housner, G.W., "Intensity of Earthquake Shaking Near the 
Causative Fault," Proceedings of the Third World Confer- 
ence on Earthquake Engineering, Wellington, New Zealand, 
1965, Vol. I, New Zealand Institution of Engineers, Welling- 
ton, 1966, pp. 111-94— III-115. 

Jennings, P.C. (Editor) , "Engineering Features of the San 
Fernando Earthquake, February 9, 1971," Earthquake Engi- 



neering Research Laboratory Report EERL 71 *\'i Cali- 
fornia Institute oi rechnol dena June- 1971 ', 

Kamb, Barclay, Silvei I I Utfasm M | Carter B.A., 
Jordan, Thomai If and Minuet | Bernai rn of 

Faulting and Nature ol Fauli Movement in \\\<- San Fer- 
nando Earthquake," The San Fernando, Califorr 
quake o\ February 9, 1971, Geological Sui < . /- 
Paper 733 U S Geological Survey and the National Oceanic 
,ni(l Atmospheric Administration, U.S. Department of the 
[nterioi and IS Department of Commerce, vVashh 
D.C., 1971, pp. 11-54. 

McNey, [en-old I. Southern California Edison 
Rosemead, Calif., 1971 (personal communication). 

Proctor, R.J.. Brooki D.C. and Pentegoff, V.P. "Explora- 
tion lor 52 Miles of 1 iintirls lor tin- Foothill Feeder," Fngi- 
neering Geology m Southern California, Association of En- 
gineering Geologists, Arcadia, Calif.. 1966, pp. 81-87. 

Proctor, R.J., Crook. R.. McKeown, M.H. and Moresco. 
R.I... "Relationship of Known Faults to Surface Ru; 
l ( )7l S;* ii Fernando Earthquake, Southern California." Bulle- 
tin of the Geological Society of America, Vol. 83, N 
June 1972, pp. 1601-1618. 

Scott, Nina H.. "Preliminary Report on Felt Area and Inten- 
sity," The San Fernando, California, Earthquake of Febru- 
ary 9, 1971 , Geological Survey Professional Paper 733, VS. 
Geological Survey and the National Oceanic and Atmos- 
pheric Administration, U.S. Department of the Interior and 
U.S. Department of Commerce, Washington, D.C, 1971, 
pp. 153-154. 

Seed, H. Bolton, University of California, Berkeley. Calif., 
1971 (personal communication) . 

U.S. Geological Survey and the National Oceanic and Atmos- 
pheric Administration (Publishers), The San Fernando, 
California, Earthquake of February 9, 1971, Geological Sur- 
rey Professional Paper 733. U.S. Department of the Interior 
and U.S. Department of Commerce, Washington, D.C, 1971, 
254 pp. 

Voud, T. Leslie. "Landsliding in the Yicinitv of the Yan Nor- 
man Lakes." The San Fernando. California, Earthquake of 
February 9, 1971, Geological Survey Professional Paper 
733, U.S. Geological Survey and the National Oceanic and 
Atmospheric Administration, U.S. Department of the Inte- 
rior and U.S. Department of Commerce, Washington, D.C, 
1971, pp. 105-109. 

Youd, T. Leslie, and Olsen. H.W., "Damage to Constructed 
Works, Associated With Soil Movements and Foundation 
Failures," The San Fernando, California, Earthquake of 
February 9, 19~1 . Geological Survey Professional Paper 733, 
U.S. Geological Survey and the National Oceanic and At- 
mospheric Administration, U.S. Department of the Interior 
and U.S. Department of Commerce, Washington. D.C, 1971, 
pp. 126-132. 



^and Movement Studies 

lelated to 

Ian Fernando Earthquake 



CONTENTS 

Page 

223 Introduction 

223 Genera! 

226 Definitions 

226 Contents of Report 

228 Part I — Work Resume of Agencies 

230 Part II — Determination of 

Horizontal Earth Movements 

230 Initial Surveys 

234 Evaluation of Apparent Movement 

235 Supplementary Surveys 

235 Part III — Determination of Vertical 

Earth Movements 

240 Part IV — Findings 

240 Conclusions 

241 General Recommendations 

242 Specific Recommendations 
242 Acknowledgments 

242 References 



DEPARTMENT OF COUNTY ENGINEER 
COUNTY OF LOS ANGELES 

Geodetic Section—Survey Division 
Los Angeles, Calif. 



INTRODUCTION 

General 

The February 9, 1971, San Fernando earthquake 
affected a metropolitan area (fig. 1) in which active 
geodetic programs were in effect by several organiza- 
tions and in which there were many first-order hori- 
zontal (fig. 2) and vertical (fig. 3) control stations 
within the area of maximum damage. Thus, redeter- 
mination of horizontal positions and elevations 
throughout the region will provide a large volume of 
quantitative data as to the direction and magnitude 
of land movements resulting from the earthquake. 

The implications of this information to the 
geodesist, topographer, and civil engineer are fairly 
clear, but the structural engineer, geologist, soils en- 
gineer, and others engaged in determinations of site 
safety and stability should likewise benefit. The im- 
plications to the land surveyor and property owner 
are discussed in the report of the Subcommittee 
on Sociological Aspects (in Volume II) . 



LOS ANGEL C01 



, Newhall 
Svlmar-X--— s~~^/ Earthquake Area 




San Fernando 



1 1 mg Beach 



Figure 1. — Maps of San Fernando earthquake area. 



223 



224 San Fernando Earthquake of 1971 



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Land Movement Studies Related to Earthquake 



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60 



226 San Fernando Earthquake of 1971 



Less than 2 hours after the majoi tremoi occurred 
at 6:01 a.m., a map reconnaissance ol available sui 
vey control was instituted wiih reliance being placed 
on fragmentary reports of damage being broadcast by 
local radio stations as to the location ol the area ol 
greatest damage (Los Angeles County Earthquake 
Commission 1071). Within \ hours, the- National 
Geodetic Survey (NGS) of the National Oceanic 
and Atmospheric Administration (NOAA) and Los 
Angeles County Engineer (LACO) had established 
contact and agreed on a tentative plan to evaluate 
horizontal movements. An NGS party was immedi- 
ately assigned to reobserve two ol the existing 
faultline-crossing networks on the San Andreas iilt. ! 
By February 11, the primary objectives ol majoi local 
agencies had been established and field observations 
had begun. Iiy February 17, a fully coordinated pro- 
gram involving all interested local agencies with sur- 
vey capabilities had been effected. At this time, 
LACO was designated as the coordinating agency. 
On March 3, 1971, I. H. Alexander, LACO, was 
invited to chair this Subcommittee on Geodesy. 

The first surveys had two primary objectives: to 
determine the gross differential movement within or 
at the visual boundaries of the area apparently dis- 
placed; and to determine the stability of damaged, 
but still standing, structures under aftershock 
stresses. Some of the data obtained under the first 
objective will be adapted and included in this re- 
port. Most of the data obtained under the second 
objective will be included in the structural engineer- 
ing sections. 

Definitions 

It is presumed that not all readers of this report 
will be trained in geodesy; hence, certain basic con- 
cepts will be detailed. 

Geodesy, as defined for this paper, refers to all sur- 
veys falling within NGS specifications for first- and 
second-order work and to such secondary and lower 
order surveys as required to give a clear picture of 
the major earth movements resulting from the earth- 
quake. 

Reference in this report to the horizontal positron 
of a point is in terms of its geodetic coordinates, lat- 
itude, and longitude. These are given with respect to 
the North American Datum of 1927 (U.S. Coast and 
Geodetic Survey 1936) . For mapping purposes, this 

i National Geodetic Survey periodic reports are published when 
reobservation data have been analyzed. These are available from 
NOAA/NGS, Rockville, Md. 20852. 



position ma\ he- transformed into a unique 
ordinate. Coordinates, where used in this report, 
refei to the California Coordinate System zone 
I S Coast and Geodetii Survey I94H and 1951 . 

Reference will U<- made- in the bod\ ol this r< 
to the Coop Net and to Coop Lines. ' Where this 
is done, the i deictic c- is to the- Southern California 
Cooperative Leveling Program (Franceschini and 
Mitchell 1969). Field work foi this Coop \< 
executed by Los Angeles, Orange, Riverside, San 
Bernardino, San Diego, and Ventura Countii 
Los ■ Angeles eitv and b) the U.S. (oast and 
dctie Sui\c-\ US< GS . The final adjustmen 
completed h\ the US< £:GS in 1970. Precise leveling 
ol 1,575 miles was included in the completed adjust- 
ment. 'I hose- poitions relating to the- San Fernando 
earthquake area an- shown in figure 1 

The- vertical positions (or elevations) ol points 
ue given with respect to the- Mean Sea Level Datum 
ol l ( ('_'!t. as established and maintained b\ N'G 
the National Ocean Sur\c\ (formerly the 1 

Because southern California is an area e)f known 
geodetic instability, dates will accompany adjust- 
ments, observations, and positions ol \arie>us monu- 
ments in main instanc c s. 

Geodetu work is performed at various levels of 
predefined results called "orders of accuracy," and an 
attempt will he made to append the appropriate 
order applying to a particular result. In all cases, 
the standards acceptable for that order will be as de- 
fined by the NGS (U.S. Coast and Geodetic Survey 
1950U 

What monuments to hold as "fixed" or "stable" in 
determining resulting movements was a primary 
question. Part II of this report discusses the prob- 
lems encountered and methods of solution. 

Contents of Report 

Part I of the report will discuss the contribution 
of each local and national agency to the geodetic 
program. Parts II and III will discuss the problems 
associated with the respective determinations of hori- 
zontal and vertical movements, while Part IV will re- 
port the findings. 

In evaluating the findings reported in Part IV. it 
must be stressed that all movements are in relation 
to some established point or datum of reference. A 
major element of the geodetic program was, and re- 
mains, the determination of an adequate base of ref- 
erence. This topic is developed in greater detail in 
Parts II and III of this report. 



Land Movement Studies Related to Earthquake 227 




V 

I 



o 

o 
O 






3 
bo 



228 



San Fernando Earthquake of 1971 



A related problem concerns the inability of 
geodesists to distinguish between long-term strain ac- 
cumulation and the sudden release of that accumula 
linn at the time of an earthquake. The receni advent 
of electronic distance-measurement equipment now 
provides tools far superior to any in existence before 
1955. It still remains, however, lor the scientific com- 
munity to obtain sufficient funds to make the needed 
measurements in the quantity and with the fre- 
quency needed. This limitation will be apparent as 
this report is considered. 

PART I-WORK RESUME OF AGENCIES 

A minimum of duplication of survey work oc- 
curred as a result of close cooperation between the 
many participating agencies. 

Each of the following listed agencies undertook 
the survey work required to determine in the best 
manner the effect the earthquake had on its facili- 
ties, improvements, or public responsibilities. 

Alphabetically, the agencies contributing to the 
geodetic study were: 

California Department of Water Resources 
California Division of Highways, District VII 
City of Los Angeles, Bureau of Engineering 
City of Los Angeles, Department of Water and 
Power 

Power Systems 
Water Systems 
Los Angeles County Engineer 
Los Angeles County Flood Control District 
Metropolitan Water District of Southern Cali- 
fornia 
National Geodetic Survey, NOAA 
Southern California Edison Company 
U.S. Army Corps of Engineers 
U.S. Geological Survey 
The specific contribution of each of these agencies 
is summarized in the following paragraphs. The in- 
terrelation between the work of the various agencies 
is explained more fully in Parts II and III of this re- 
port. 

California Department of Water Resources 
(CDJVR). Leveling was completed along the CDWR 
Aqueduct from San Bernardino County through 
Palmdale in Los Angeles County northwesterly into 
Kern County. This line is shown as the "CDWR 
Aqueduct" in figure 5. Many NGS and LACO pre- 
cise bench marks were used. Elevation differences 



indie ;itc- ;i maximum variance of 0.04 foot be -• 
190') preearthquake and 1971 postearthquake field 

work. 

California Division of II / ,. 1) \rici 111 
i(l)ll I II). Extensive losses occurred to the 
highway network adjacent to the- Sylmai San Fer- 
nando area. Realizing that major demolition, rede- 
sign, and reconstruction would be required, the Dis- 
trict VII survey forces completed secondary 
triangulation from Castaic into the San Fernando 
area (fig. 6). Directly affected were Interstate High- 
ways 5, 210, and 10~< and California Highway Route 
14. 

City of Los Angeles, Bureau of Engineering 
(LABI). Extensive stn\e-\s were undertaken to assist 
in determining amounts and locations of land : 
ment. (Geodeti< surveying consisted of releveling 
from Tidal Bene h Mark No. 8 at Los Angeles Harbor 
into the S:in Fernando area along Coop Lines 301, 
305, 307, and 308 as shown in figure 4. Triangula- 
tion and traverse surveys were completed and will be 
connected to the primary control net as shown in 
figure 7. Movement data of selected stations within 
the shaded area in figure 7 are tabulated in table 3. 
Additional surveys are continuing and, while not a 
part of the geodetic program, will assist in defining 
the area of movement and will indicate movements 
affecting owners of property in the area. Control sur- 
veys were performed by the LABE Central Office, 
while other surveys were done by the Van Xuvs 
District Office. 

City of Los Angeles, Department of Water and 
Power (LADWP). 

Power Systems (LADWP-P) . A traverse was 
run along transmission lines from Sylmar to Haskell 
Canyon before the earthquake. This same traverse 
was rerun after the earthquake. For coordinate con- 
trol, triangulation stations View and Haskell were 
held fixed. 

Water Systems (LADWP-W) . Major damage 
at the Van Norman Reservoir focused the activities 
of this agency on the horizontal and vertical control 
in the vicinity of the reservoir as shown in figures 2 
and 8. The reservoir area has been remapped using 
photogrammetric methods, based upon postearth- 
quake local ground control (fig. 8) . Because the pri- 
mary control net was not complete, it was not possi- 
ble to relate this mapping to the national net as 
would have been desirable. 



Land Movement Studies Related to Earthquake 229 



' <: i 



KERN COUNTY 



YXGrap 



O Mojave 



) Rosamond 






GormanO* 205 



NGS 



-®U 



^< 



VENTURA COUNTY 



te 



$ 



Palm dale 



--0- 



._-' Wo, 



\ V 

» ^06,-->~^Castaic,x / 



,- --2P.5-.--' 



Pearblossom • 

^ V 



°°DOOO a oD° D 



LOS ANGELES COUNTY 



Oy-^Sylmar 



K K>o 






£)Azus 



Los Angeles I I g* 

Civic Center L-J° ODODOoD ° 

o o 12 & 16 (L.A. Co.) 
ooa D 




tf 



rJ 



PACIFIC OCEAN 



J 

ORANGE COUNTY 



\ 



\ 



LEGEND: 

National Geodetic Survey 

ooooooo L.A. County Engineer 

oooooo L.A. City Bureau of Engineering 



Scale in miles 



Hgure 5. — Precise postearthquake leveling nets, southern California, December 1971. 



Los Angeles County Engineer (LACO). Field 
reconnaissance started immediately after the earth- 
quake. The primary triangulation net (fig. 9) was 
developed and observed cooperatively with NGS. 
The LACO Llano Base Line in Antelope Valley was 
retaped to provide a length standard for all elec- 
tronic distance-measuring equipment. Precise level- 
ing was delayed until major aftershock activity had 
diminished. Early in March 1971, the leveling shown 
on figure 5 was started. Other nongeodetic, but 



earthquake-related, activity has included work at the 
county's damaged Olive View Hospital to check the 
effects of aftershock activity on building stability. As- 
sistance was given to the NGS in its precise leveling 
and gravity measurement activities. Close coordina- 
tion between LACO and NGS greatly facilitated the 
observations and adjustments of the primary control 
net. 

Los Angeles Comity Flood Control District 
(LACFCD). Immediately after the earthquake, 



230 



San Fernando Earthquake of 1971 




Figure 6. — Earthquake study area (shaded). 
California Division of Highways District VII. 

LACFGD reran levels along the District's channels in 
the San Fernando— Sylmar area to determine major 
elevation changes. Later, they ran precise levels 
along these channels and made ties to LABE and 
LACO bench marks where available. Deformation 
studies, both horizontal and vertical, using first-order 
observing methods and equipment were undertaken 
at Pacoima and Big Tujunga Dams and are discussed 
in the section on Water and Sewerage Systems (in 
Volume II) . Direct survey connection of these study 
sites to the primary control net was not considered 
necessary. 

Metropolitan Water District of Southern Cali- 
fornia (MWD). The primary concern of MWD was 
to determine the effect of the earthquake on the 
Joseph Jensen Filtration Plant, west of Interstate 5 
and north of the Van Norman Reservoirs (fig. 2) . 
Horizontal and vertical work was completed based 
upon a local datum. Survey work was continued at 
the filtration plant site to monitor the effects of the 
aftershock activity. Length changes of record survey 
lines were noted by MWD, but were not directly 
connected to the national net. 

National Geodetic Survey (NGS). A high prior- 
ity has been given to all work associated with the 



l<l, i ii.u y 9 1971 earthqual i detu p 

were assigned to worl cooperatively with J 
Releveling was completed along Loop Lines 102, 
'200, 200, 207, and along portions ol Loop Lines 100 
and 20") (fig. 5) . Vgain this was a cooperative pi 
with LABE and LACO assisting. A gravimetric party 
was assigned to make gravity determinations along 
the lines ol precise leveling. I h<- extern ol the pri- 
mal \ horizontal control net is shown in figure 9. 

Southern California Edison Company ( 
Data have been compiled showing differential movel 
uiciii along the Sylmai Gould 220-kv and the Svlrnar 
Tap Transmission Lines. J his was a Tellurometei 
and Wild 1-2 Theodolite traverse survey peilormed 
by SCI LACO has located each end of this traverse 
with respeel to stations ol the primary control net, 
enabling movement data to be determined whenever 
the primal y < ontrol net data bee ante av ailable. 

U.S. Army Corps of Engineers (USCE). Survey 
activities have consisted ol leveling in the Wilson- 
Mansfield Channel and of damage survevs of im- 
provements in the vicinity ol Lopez Canyon and the 
San Fernando Reservoir. 

U.S. Geological Survey <TSCS;. The National 
Center for Earthquake Research in Menlo Park, 
Calif., took an active role in determining land move- 
ments in the 2 weeks immediately following the 
earthquake. The Topographic Section dispatched 
leveling parties to the Sylmar-San Fernando area 
and performed leveling from February 11 to April 
11, 1071. Portions of this leveling supplement the 
geodetic leveling. 

The following additional agencies — California Di- 
vision of Mines and Geology. Los Angeles County 
Road Department, and U.S. Forest Service — were 
contacted regarding involvement in the geodetic sur- 
vey program. No precise work is contemplated by 
them as a result of the earthquake. 

PART II-DETERMINATION OF HORIZON- 
TAL EARTH MOVEMENTS 

Initial Surveys 

Reconnaissance was started immediately after it be- 
came apparent that major surface displacements had 
occurred as a result of the February 9 earthquake. 
An abundance of existing control permitted a high 
degree of freedom in selecting and planning an ob- 






Land Movement Studies Related to Earthquake 231 




8 

hi 






■a 
S 






232 San Fernando Earthquake of 1971 




Grapevine 



Scale id feet 
Note: Length changes in feel 



Figure 8. — Typical example of line-length changes for determination of earthquake differential movement data. 
Water Systems, Los Angeles City Department of Water and Power. 



servation program. This survey resume will relate to 
the work of the four primary agencies; namely, 
USGS, NGS, LABE, and LACO. 

While major aftershocks were still occurring, the 
USGS obtained line-length changes on 18 lines 
within the area of major damage and on seven lines 
to points outside the area. These changes resulted 
from a comparison of line lengths determined from 
preearthquake-published positions and from post- 
earthquake direct measurements (table 1) . Figure 9 
shows the location of these stations. 

The postearthquake observations initially were re- 
duced using incomplete vertical data. They were 
published less than 3 weeks after the earthquake. In 
subsequent months, these reductions were refined 
and are those now shown in Savage et al. (1972) . 
Both postearthquake values are shown in table 1 and 
illustrate the magnitude of uncertainty that may be 
introduced using incomplete data. There will not be 



an attempt here to make the corresponding compari- 
son with preearthquake-published versus postearth- 
quake-published lengths or with preearthquake- 
unconstrained versus postearthquake-unconstrained 
lengths. 

The measurements shown in table 1 were made 
using a Geodolite. The atmospheric corrections ap- 
plied were based on observations taken in a helicop- 
ter flying along the line of sight at the time of meas- 
urement. Additional measurements had been planned. 
but were curtailed when a chansre in weather condi- 

o 

tions prevented further helicopter flights. 

Many surface failures (upheavals or cracks) were 
visible for examination by geophysicists and geolo- 
gists. The first data to be released regarding land 
movements appeared in a preliminarv USGS report 
dated March 3, 1971. Close cooperation between 
USGS and LACO was accomplished. 

The LABE also undertook distance measuring be- 



Land Movement Studies Related to Earthquake 233 



+ 34°45 
118°45' 




+ 34°5' 
118°45' 
NOTE: 

The numbering of stations shown 
relates to main net and insert map 



118°30' 



118°15' 



34°15' 



12 4 f 34°5' 

^ ■" 118°0' 
Scale in miles 

Not used in Triangulation Net 



Figure 9. — San Fernando earthquake primary triangulation net. See index of triangulation stations in table 5. 
Los Angeles City Bureau of Engineering, National Geodetic Survey, and Los Angeles County Engineer. 

tween certain existing control monuments to deter- shown at reduced scale as an insert in figure 9. Ob- 
mine differential movement data. servations were initiated at stations Hauser and Pe- 
A primary net extending from the crest of the lona by NGS and at stations Cahuenga and Calabasas 
Santa Monica Mountains northward to the vicinity by LACO. 

of Gorman was devised by LACO and submitted to Preliminary checks on the position of station Sister 

NGS for review and comment. This first net is Elsie prompted the addition of stations in the vi- 



234 San Fernando Earthquake of 1971 



Table l.—Lirw length ihangei 
[Determined by ' S < ,■ Aogical Survey; mea- 





(1) 


'2; 










Lines and limiting points 




I'm liminary 




1 inal 








irthquake postearthquake 


length 


take 


line U 






distant - 


distance 2 


i ha 






iintv * 














Pacoima L-l to: 
















4511.72 


4510 47 


-1 20 


4510.475 


-1 24 




Sylmar F-8 


6708.68 


6707.11 


-1 57 


6707 098 


-1 


-0.01 


PAC E-2 ECG 1 


5141.72 

322'. 


5139 66 
3229.27 


-2 


51 '/< 

• 22', 


-2.06 

-0 10 


00 




-0 04 




6951 .26 

5444.05 


6949 82 

5442.77 


-1 44 
- 1 28 




-l 32 

-. 


- 12 




f 


PAC E-2 ECC 1 to: 
















5454.10 


5453.75 


-0 35 


5453.719 


-0 38 


-0 03 


Pacoima No. 2 


5728.76 


5728 57 


-0 19 


5728 552 


-0.21 


-0 02 


Sylmar 1-12 


3 1 50 . 74 


3149 94 


- (l 


3149 


-0 79 


. 


Reservoir 


2420.21 


2420 62 


> 41 


242'. 


+0 


-0 03 




7572.70 


7 _ ,72 35 


-0 15 


7 572 334 


-0.37 


-0 02 




8116 I'. 


81 It, 46 


. ii 


8116 


1 29 


-0.01 




7048.57 


7048.97 


4-0.40 


7048 978 


-0 41 




Bluff 


7256 39 


7 256. 74 


, 


707 


. 12 


-0 03 


Calabasas 


23689.20 


23689.42 


+0.22 








Sylmar F-8 to: 














Sylmar 1-12 


4063.59 


4063.04 


-0.55 


4063.147 


-0.44 


-0.11 


Reservoir 


5918 


5918.58 


4-0.08 


5918 


4-0.04 


-0.04 


PAG E-2 ECG 1 


i 90 
9268.57 


5354.95 
9268. V 


f-0.05 
-0.20 


5354.932 

9268 301 


-0.27 


-0 02 


Pacoima No. 2 


-0.07 


Bluff 


9643.56 


9643 '-2 


-0.04 


9643.450 


— 0.11 


-0.07 


Mays 2 


2719.77 


2719.60 


-0.17 


2719 620 


-0.15 


-0.02 




4406.76 


4406 2 1 


-0.53 


4400 161 


-0.60 


-0.07 


May 


2874.85 


2874.95 


. 10 


2874.638 


-0.21 


-0.31 


Mission Point 


7776.93 


7776.93 


00 


777»,.907 


-0.02 


-0.02 






1 Calculated from published positions. 




5 Later refined reductions. 






2 Reduced using incomplete vertical data. 




4 Uncertainty that 


can be introduced 


by using incomplete data. 



cinity of Mt. Wilson, Mt. Gleason, and Pacifico 
Mountain. Stations Flint and Verdugo were added at 
this time to provide connections needed by LA BE in 
its connection to the primary net. 

The arc of smaller figures extending northward 
from station Corner was added by NGS to 
strengthen the net and to provide information on 
crustal movements in the Newhall-Sauarus area. 

O 

Other modifications were made as the work pro- 
gressed, and the final net is shown in figure 9. 

These additions added greatly to the value of the 
completed net, but, at the same time, increased the 
amount of field time required for the survey. The 
field work was greatly expedited by a cooperative in- 
terchange of personnel and equipment between NGS 
and LACO. This interchange was accomplished at 
the survey party level, thereby permitting the maxi- 
mum freedom to cope with the ever-changing re- 
quirements of field operations. 

The only large-scale photography known to have 
been taken immediately after the earthquake was 
taken for news purposes and for damage assessment 
in particular areas. High-altitude photogrammetric 
coverage was taken by the Aerospace Charting and 



Geodetic Service ol the L'SGS immediately following 
the earthquake (Anonymous 1971). The precision 
now obtainable by analytical methods suggests that 
much data desired in the early stages ol the investiga- 
tion could have been obtained by this method and 
later refined as the geodetic survey was completed. 

Evaluation of Apparent Movement 

To evaluate the significance of movement vectors 
derived from posteai thquake observations, it is neces- 
sary to make a detailed examination of the signifi- 
cance of the published preearthquake positions of 
the affected stations. 

The primary geodetic control in the Los Angeles 
Basin was based on field work performed in 1934. 
Thirty-eight stations were included in the first local 
establishment of geodetic control. In this classic ad- 
justment, the following NGS stations were held 
fixed: Castro, 1898; San Fernando, 1898; San Pedro, 
1853; Los Angeles Northwest Base, 1889; and Wilson 
Peak, 1890. The resulting positions of stations in this 
net were published by the U.S. Coast and Geodetic 
Survey (1936). 



Land Movement Studies Related to Earthquake 235 



As new surveys were established throughout Los 
Angeles County, USC&GS was forced to fit the posi- 
tions of stations previously determined. This resulted 
in some distortions, and, in recent years, some prob- 
lems were encountered in obtaining satisfactory clo- 
sures between positions determined previously. To 
resolve these problems, a simultaneous adjustment of 
the primary network of stations was performed by 
NGS in 1970. This readjustment included the pri- 
mary geodetic control stations north of the San Ga- 
briel Mountains in Los Angeles County and some 
stations in adjacent counties. Results of this readjust- 
ment were adopted by LACO, and these values will 
supersede the previously adjusted positions in NGS 
files. 

The network of stations observed in the postearth- 
quake surveys is shown in figure 9. After a careful 
review of the observational data by NGS, it was 
found that observed angles at the exterior stations 
(fig. 9) were in very close agreement with the 
preearthquake values. An adjustment of this net was 
then made by NGS, holding positions of the exterior 
stations fixed. The adjusted positions of the interior 
stations will be added to the files of NGS, and these 
data will carry the note: "This position to be used 
in surveys performed after the earthquake of Febru- 
ary 9, 1971." 

The vectors shown in figure 10 indicate the shift 
from preearthquake positions of 1970 to postearth- 
quake-constrained positions for the various stations. 
The vectors are based on position data for these and 
other stations shown in table 2. The reader is cau- 
tioned that these positions and vectors reflect not 
only earthquake movement, but also reflect any of the 
adjustment uncertainties of both the preearthquake 
and postearthquake data. These adjustment uncer- 
tainties are introduced when the survey networks are 
made consistent with previously determined posi- 
tions on the North American Datum of 1927. In the 
1970 readjustment of the Los Angeles County net- 
work, stations which were held fixed alone: the north- 
em extremity were about 20 miles north of the 
county boundary. Using the selected control stations 
along the southern part of the network, the computa- 
tions showed a closure of 8 feet (about one part in 
50,000) south to north across the area. There was no 
significant closure in the east-west direction. 

To absorb the 8-foot closure in latitude, the 
preearthquake- and postearthquake-constrained ad- 
justed distances increased in the north-south direc- 



tion. The magnitude of these length changes, except 
for the extreme northern part of the area, is on the 
order of one part in 75,000. 

The positions obtained from these constrained ad- 
justments of the preearthquake and postearthquake 
surveys will, however, be adopted by local agencies 
for engineering purposes and will be used for con- 
trol to determine shifts of property lines, street cen- 
terlines, and other works of man both public and 
private. 

To obtain the best possible data for horizontal 
earth movement studies, it is necessary to eliminate 
the adjustment uncertainties from the results. This 
is done by making free adjustments of the preearth- 
quake and postearthquake surveys. In a free adjust- 
ment, there are no constraints to force the observa- 
tional data to fit previously determined positions. 
Free adjustments have been performed by geodesists 
of NGS, and the results are discussed in Volume III 
in the paper, "Horizontal Crustal Movements De- 
termined From Surveys After San Fernando Earth- 
quake" by Meade and Miller. 

Supplementary Surveys 

Within the framework of the primary nets de- 
scribed above, LABE has executed first-order control 
surveys within the area indicated by shading in 
figure 7. LABE will continue first-order traverse 
and second- and third-order traverses along all city 
streets in the earthquake area. Even with the com- 
mitment of five or more survey parties to this work, 
the traverse work is expected to continue into 1973. 

Second-order surveys were made by CDH-VII in 
the Santa Clara River area. The location of these 
surveys is indicated by the shaded portion of figure 6. 

Residts of these local agency control surveys will 
be available from the agency or from LACO and 
will be consistent with the data shown in tables 2 
and 3. 

PART III-DETERMINATION OF VERTICAL 
EARTH MOVEMENTS 

In June 1970, the results of the Southern Califor- 
nia Cooperative Leveling Program — Coop Net — 
(U.S. Coast and Geodetic Survey 1970) 2 were made 
available (fig. 4) . The Coop Net was the result of a 

2 Data are available from National Geodetic Survey, National 
Ocean Survey, National Oceanic and Atmospheric Administration, 
Rockville, Md. 20852. 



236 San Fernando Earthquake of 1971 



U8°45' 



: ! IS 
19 



-34°15' 








54 A 






O M 






55 











53 


58 
57 . 28^ 


1IJ 


fi 


<£> 59 8 


. 15 


.24 




o— • 


02 
51 


56 -*J 

^ ,.44 61 

6 V 52 

f 39 

I « 
t° 38 \ 


9 


& 









A 29 

.-. 
30 










44 
45 



•-O Q 

13 '•-" 



N61° .88, 

25 ,b San 27 / 2 ' M 
26 Fernando 



Granada Hills 63 



11 



+ 34°5' U8°30' 

118°45' 

LEGEND 

A» Held Fixed in Position 
*-0 - Movement Vector 

Only movements greater than 0. 20 foot shown 



- 34=5' 
11*0' 



Scale in miles 
Vector movement in feet 



Fieure 10.-Apparent horizontal movement at survey control stations resulting from 
constrained adjustment by National Geodetic Survey. 



Land Movement Studies Related to Earthquake 237 



Table 2.— California Zone 7 coordinates and coordinate change data resulting from National Geodetic Survey constrained adjustment, 

regarding San Fernando earthquake 

[Determinations made by Los Angeles County Engineer] 



Station name 



LACO 
no. 



Popular name 



NGS 
no. 



Date 



California Zone 7 coordinates 



ACR H-3 . 
ACR H-3 . 

ALTA-5. 
ALT A-5. 



BPK H-7 . 
BPK H-7 . 

BURJ-8. 
BURJ-8. 



CASD- 
CASD- 



CHAH-6. 
CHA H-6. 



DCG-8. 
DCG-8. 



GV A-10. 
GV A-10. 



GVC 
GVC 



■12. 
-12. 



GVD-9. 
GVD-9. 



LCR C-l 1 AUX 1 
LCRC-11 AUX 1 



LCR H-4 . 
LCRH-4. 



LTI-2. 
LTI-2. 

LTJ-2. 

LTJ-2. 



MTG B-2 . 
MTG B-2 . 



MTW E-10A. 
MTWE-10A. 



NH B-6. 
NHB-6 

NH C-l . 
NH C-l . 



NH E-10B. 



NH H-l 
NH H-l 



NH H-3 . 
NH H-3 . 

NH 1-1 1 . 
NH 1-1 1 . 



NH J-8 . 
NHJ-8. 



PACB-7. 

PAC C-l . 
PAC C-l . 



PAC E-2 ECC 1 
PAC E-2 ECC 1 



01 
01 

02 
02 

03 
03 

04 
04 

05 
05 

06 
06 

07 
07 

08 
08 

09 
09 

10 
10 

11 
11 

12 
12 

13 
13 

14 
14 

15 
15 

16 
16 

17 
17 

18 
18 



20 
20 

21 
21 

22 

22 

23 
23 



25 
25 

26 

26 



Pacifico. 
Pacifico . 



Flint. 
Flint. 



Sawmill . 
Sawmill . 



Cahuenga 2. 
Cahuenga 2. 



Loma Verde . 
Loma Verde . 

Chatsworth . . 
Chatsworth . . 



Calabasas . 
Calabasas. 



Brushy . 
Brushy . 



Deer. 
Deer. 



House . 
House . 



Verdugo AUX . 
Verdugo AUX. 



Sister Elsie. 
Sister Elsie. 



Port. 
Port. 



Magic . 
Magic . 



Towsley . 
Towsley . 



Lock. 
Lock. 



19 Ridge 2. 



Newhall . 
Newhall . 



Edison No. 2 . 
Edison No. 2. 



Mission Point . 
Mission Point . 



East. 
East. 



24 Darling. 



Reservoir 1932. 
Reservoir 1932 . 



N4 
N4 

N4 
N4 

N4 
N4 

N4 
N4 

N 4 
N4 

N4 
N 4 

N4 
N 4 

N4 
N4 



N4 

N 4 
N4 



212 1970 
724 1971 
Position held fixed 
1968 

719 1971 
Position held fixed 

112 1970 
768 1971 
Position held fixed 
1915 

717 1971 
Position held fixed 

080 1970 

764 1971 

Position held fixed 

1967 

703 1971 

Position held fixed 

1965 

701 1971 

Position held fixed 

021 1970 
754 1971 

Coordinate change 0.28 ft 
102 1970 N 4 

752 1971 N4 
Coordinate change 0.45 ft 

022 1970 N 4 

753 1971 
Position held fixed 

1967 

718 1971 
Coordinate change 0.42 ft 

903 1970 N 4 

721 1971 N4 

Coordinate change 1 .03 ft 

187 1970 N 4 
732 1971 N4 

Coordinate change 0.38 ft 

188 1970 N 4 
731 1971 N4 

Coordinate change . 28 ft 

1961 N 4 

727 1971 N4 

Coordinate change 0.22 ft 
1970 N 4 

720 1971 
Position held fixed 

008 1970 

740 1971 
Coordinate change . 66 ft 

010 1970 N4 

742 1971 N 4 

Coordinate change 1.04 ft 
713 1971 N4 

New station 

009 1970 N 4 

741 1971 N 4 
Coordinate change 1 .00 ft 

007 1970 N 4 

739 1971 N4 

Coordinate change 0.88 ft 
004 1970 N 4 

712 1971 N4 

Coordinate change 0.40 ft 
273 1970 N 4 

735 1971 N4 

Coordinate change . 34 ft 
1954 N4 

Station not recovered 

001 1970 N 4 

709 1971 N 4 

Coordinate change 0.61 ft 

1961 N4 

706 1971 N 4 



N4 

N4 

N4 



251,503.65 
251,503.65 

171,957.93 
171,957.93 



364,741 
364,741 



93 
93 



162 
162 



250.30 
250.30 



293,191 
293,191 



50 
50 



206,090.37 
206,090.37 

163,510.85 
163,510.85 

310,995.34 

310,995.26 

S73-30W 

306,232.96 

306,232.97 

N88-44E 

315,051.68 

315,051.68 



.68 
.08 



190,541 

190,542. 

N18-00E 

210,310.05 

210,310.89 

N35-05E 

253,006.80 

253,006.75 

S82-30W 

252,946.57 

252,946.29 

S02-03E 

253,220.48 

253,220.44 

S79-42W 

193,514.03 

193,514.03 

242,086.22 

242,086.88 

N05-12E 

255,886.93 

255,887.96 

N06-06W 

229,019.62 

255,938.76 

255,939.67 

N24-15W 

249,031.45 

249,032.29 

N17-12W 

225,899.79 

225,900.19 

N00-00 

237,725.46 

237,725.79 

N13-38W 

201,820.88 

218,584.73 

218,585.11 

N51-38W 

217,792.36 

217,792.54 



E4 
E4 

E4 
E4 

E4 
E 4 

E4 
E 4 

E 4 
E4 

E4 
E4 

E4 
E4 

E4 
E 4 

E 4 
E 4 

E 4 
E4 

E4 
E 4 

E 4 
E 4 

E4 
E4 

E4 
E4 

E4 

E 4 

E4 
E 4 

E 4 
E 4 

E 4 
E4 

E4 

E4 
E 4 

E4 
E4 

E4 
E 4 

E 4 
E 4 

E4 

E4 
E4 

E 4 
E4 



Coordinate change 0.88 ft N 78-1 IE 



277,110.25 
277,110.25 

228,288.79 
228,288.79 

118,406.66 
118,406.66 

189,241.55 
189,241.55 

085,929.87 
085,929.87 

094,114.20 
094,114.20 

092,459.23 
092,459.23 

136,775.88 
136,775.61 

143,192.56 
143,193.01 

145,558.02 
145,558.02 

202,675.88 
202,676.01 

215,472.08 
215,472.67 

188,052.07 
188,051.69 

191,495.82 
191,495.83 

231,803.77 
231,803.55 

268,814.78 
268,814.78 

109,216.52 
109,216.58 

111,592.27 
111,592.16 

116,958.28 

125,944.80 
125,944.39 

125,755.46 
125,755.20 

126,424.10 
126,424.10 

130,426.39 
130,426.31 

139,949.50 

140,181.12 
140,180.64 

148,081.52 
148,082.38 



238 San Fernando Earthquake of 1971 



Table 2.— California lone 7 coordinates antl coordinate change data resulting from National GeodrtM Survey constrained i,<i)., 

regarding San Fernando tarthquakt Continued 

[Determinations made by Lot Deer] 



Station name 



PAG I. I 
PAC L-l. 

PAC L-5. 
PAC L-5. 



PIC L-9 AUX 2 KCC 1 
PIC L-9 AUX 2 KCC 1 



PIC L-9A. 
PIC L-9 A. 



RAVJ-5. 
RAVJ-5. 



RAVJ-5 AUX 2. 
RAVJ-5 AUX 2. 

RESK-9 



RESK-9A. 
RESK-9A. 



RR E-10. 
RR E-10. 



SAU C-9. 
SAU C-9. 

SAU D-5. 
SAU D-5. 

SAU E-3 
SAU E-3. 

SAU F-l . 
SAU F-l . 



SAU G-8A. 

SAU H-5 . . 
SAU H-5 . . 



SAU H-ll 
SAU H-ll 



SAU J-2 . 
SAU J-2 . 



SV C-8 . 
SV C-8 . 



SV C-8 ECC 2 . 
SV C-8 ECC 2. 



SYL F-8 . 
SYL F-8 . 



SYL 1-6 . . 
SYL 1-6 . . 

SYL 1-12. 
SYL 1-12. 



VVPK A-7A . 
VVPK A-7A . 



WPK A-7A AUX 1 
VVPK A-7A AUX 1 



WPK N-15. 
WPK N-15. 



WSM B-13. 
WSM B-13. 



LACO 

no. 



Popular name 



27 
27 

28 

28 

29 
29 

30 
30 

31 
31 

32 
32 



34 
34 

35 
35 

36 
36 

37 
37 

38 
38 

39 
39 



41 
41 

42 
42 

43 
43 

44 
44 

45 
45 

46 
46 

47 
47 

48 
48 

49 
49 

50 
50 

51 
51 

52 
52 



Pacoima No. 2 
Pacoima No. 2 . 



San Fernando AUX 2 I ' ' I 
San Fernando MX 2 ECH I 



Parker 
Parker 



Parker AUX 2. 
Parker AUX 2. 



33 San Vicente. 



Mauser. 
Hauser. 

Yucca . . 
Yucca. . 



Long. 
Long. 

Bum. 
Bum. 

Steer. 
Steer. 



40 Foot 2 . 



Dry. 
Drv. 



Saugus . 
Saugus . 



View. 
View . 



Pelona . 
Pelona . 



Pelona ECC 2. 
Pelona ECC 2. 



May. 
May. 



Whitaker. 
Whitaker. 



Whitaker AUX 1 
Whitaker AUX 1 



Cast C . 
Cast C . 



Fork. 
Fork. 



no. 



Dab 



Califbrni; 'late* 



N 4 

N 4 
N 4 

N 4 
N 4 



N 4 

N 4 

N 4 

N 4 

N I 



■ N 4 
705 1971 N 4 

','> ft 

1 9 ) » N 4 

715 1971 Nt 

Coordinate change 2 54 ft 

1970 N 4 
7 57 1971 

■,on held fixed 
1970 

736 1971 

•ion held fixed 
189 1970 

730 1971 

Coordinate chanf- 19 ft 

1970 N 4 

726 1971 N 4 

Coordinate chant"- 0.19 ft 
1950 N 4 

Station not recovered 

■ Nt 
702 1971 

Position held fixed 
186 1970 

729 1971 

Position held fixed 
012 1970 

744 1971 
Coordinate change 0.93 ft 

014 N 4 

746 1971 N 4 
Coordinate change 0.61 ft 

016 1970 N 4 

748 1971 N 4 
Coordinate change 0.64 ft 

018 1970 N 4 

750 1971 N 4 

Coordinate change 0.44 ft 

745 1971 N 4 
New station 

015 1970 N4 

747 1971 N 4 
Coordinate change 0.72 ft 

011 1970 N4 

743 1971 N 4 

Coordinate change 0.94 ft 

017 1970 N4 

749 1971 N 4 
Coordinate change 0.52 ft 

179 1970 N4 

734 1971 
Position held fixed 
1970 

733 1971 
Position held fixed 
1935 

704 1971 

Coordinate change 0.65 ft 

902 1970 N 4 

738 1971 N 4 

Coordinate change 0.48 ft 

1936 N 4 

707 1971 N4 

Coordinate change 3.18 ft 

103 1970 X4 

765 1971 
Position held fixed 

1970 

766 1971 
Position held fixed 

082 1970 

760 1971 
Coordinate change 0.35 ft 

084 1970 N4 

761 1971 N4 
Coordinate change 0.33 ft 



N 4 

N 4 

N 4 

N 4 

N 4 



N 4 

N 4 

N4 

N 4 

N4 



97 "'A 

. ow 

206,317 74 
20 03 

232,409 17 
232,409 17 

279,7% 18 

• BW 
740.19 

;o oo 
58W 
34 1 7 

20.44 
20.44 

311,746 41 
311,746.41 

268 . B " 
268.856.52 
N01 r ,lW 
281 ,37 
281,371 16 
N00-56E 
286,87 

78.09 

28E 
293,645.47 
293,645.91 

29E 
272,169.10 

280,838.80 

280,839.50 

N14-25W 

263,991.35 

263,992.21 

N23-17W 

291.300.57 

291.301.02 

N30-01W 

316,559.11 

316,559.11 

316,398.53 
316,398.53 

235.236.24 

235,236.82 

N27 21 W 

240,603.85 

240,603.59 

S56-59W 

223,582.55 

223,583.71 

N68-36W 

319,196.91 

319,196.91 

319,156.73 

319,156.73 

295,178.04 

295.177.83 

S53-08W 

302,594.09 

302,593.86 

S46-13W 



E 4 

I. 4 

I. I 

1. 4 
I. 4 

E4 
E 4 

E 4 

I 4 
I. 4 

E 4 
E 4 

E4 
E 4 

E 4 

E4 

E4 
E4 

E4 
E 4 

E4 

E4 
E 4 

E4 
E4 

E4 
E4 

E4 

E4 

E 4 

E 4 

E 4 
E4 

E4 

E 4 

E 4 
E 4 

E4 
E 4 

E 4 
E4 

E4 
E 4 

E 4 
E 4 



• 4 44 

106,1 

106, I'll. 58 

106,2! 

221 ,4' 
221,49 

221.517.92 
221,517.81 

222,442 44 
222,442.44 

112,354 55 
112,354.52 

114,' 
114,564.00 

116,652.49 
116,652.54 

121, . 
121,322.49 

123,913.82 

124,414.35 
124,414.17 

124,576.91 
124,576.54 

131,118.19 
131,117.93 

180.130.88 
180,130.88 

180,148.43 
180,148.43 

150,169.27 
150,168.97 

157,924 81 
157.924.41 

156,644.61 
156,641.65 

063,679.77 
063,679.77 

063,699.51 
063,699.51 

095.671.70 
095.671.42 

101,663.43 
101,663.19 



Land Movement Studies Related to Earthquake 239 



ible 2.— California Zone 7 coordinates and coordinate change data resulting from National Geodetic Survey constrained adjustment, 

regarding San Fernando earthquake— Continued 

[Determinations made by Los Angeles County Engineer] 



Station name 



LACO 
no. 



Popular name 



NGS 
no. 



Date 



California Zone 7 coordinates 



SM C- 

SMC- 



SMF-4. 
SMF-4. 

SMF-6. 
SM F-6 



SMF- 
SMF- 



13A. 
13A. 



SMH-10. 
SMH-10. 



SMJ-8. 
5MJ-8. 



5MK- 
3MK- 



SM M-5. 
;M M-5. 

SMN-13. 
SMN-13. 



,LH-2. 

iLH-2. 



LI-6D. 
;LI-6D. 



53 
53 

54 
54 

55 
55 

56 
56 

57 
57 

58 
58 

59 
59 

60 
60 

61 
61 

62 
62 

63 
63 

64 
65 



085 1970 N4 

762 1971 N4 

Coordinate change 0.24 ft 

101 1970 N4 

767 1971 N4 

Position held fixed 

087 1970 N4 

763 1971 N 4 

Coordinate change 0.1 1 ft 

083 1970 N4 

757 1971 N4 

Coordinate change 0.34 ft 

086 1970 N4 

758 1971 N4 

Coordinate change 0.28 ft 

088 1970 N4 

759 1971 N4 

Coordinate change 0.13 ft 

020 1970 N4 

756 1971 N4 

Coordinate change 0.02 ft 

081 1970 N 4 

755 1971 N 4 

Position held fixed 

019 1970 N4 

751 1971 N 4 

Coordinate change 0.26 ft 

003 1970 N4 

711 1971 N 4 

Coordinate change 0.67 ft 

002 1970 N4 

710 1971 N 4 

Coordinate change 1.17 ft 

Mays 2 Not a part of the primary 

Mesa Not a part of the primary 



Daires 

Daires 

Warm Springs. 
Warm Springs. 

Necktie 

Necktie 

Charlie 

Charlie 

Taylor 

Taylor 

Elizabeth 

Elizabeth 

Powerhouse. . . 
Powerhouse . . . 

Red 1932 

Red 1932 

Rock 

Rock 

Bluff 

Bluff 

Corner 2 

Corner 2 



310,377.60 

310,377.44 

S48-22W 

329,228.22 

329,228.22 

322,858.33 

322,858.25 

S41-11W 

300,655.75 

300,655.52 

S47-23W 

310,195.22 

310,194.98 

S32-OOW 

317,298.91 

317,298.81 

S41-59W 

306,630.96 

306,630.98 

N26-34W 

325,929.75 

325,929.75 

300,769.89 

300,770.03 

N57-32W 

217,040.36 

217,040.98 

N22-45E 

206,243.59 

206,244.41 

N45-21E 

net 



E 4, 106,280.94 
E 4, 106,280.76 



E4 
E4 

E4 
E4 

E4 
E4 

E 4 
E4 

E4 
E4 

E 4 
E4 

E4 
E4 

E4 
E4 

E4 

E4 

E4 
E4 



112 
112 

112 
112 

111 
111 

118 
118 

122 
122 

125 
125 

129 
129 

132 
132 

124 
124 

130 
130 



794.68 
794.68 

110.37 
110.30 

562 . 1 1 
561.86 

327.56 
327.41 

400.01 
399.92 

020.15 
020.14 

659 . 76 
659 . 76 

104.62 
104.40 

286 . 54 
286.80 

385.05 
385.88 



ible 3.— California Zone 7 coordinates and coordinate change data resulting from National Geodetic Survey constrained adjustment, 

regarding San Fernando earthquake 

[Determinations made by Los Angeles City Bureau of Engineering] 
Station name Date California Zone 7 coordinates 

LCRA-7 1958 N 4,202,553.62 E 4, 196,772.91 

LCRA-7 1971 N 4,202,554.50 E 4, 196,772.91 

Coordinate change 0.88 ft North 

LCR B-10A 1957 N 4, 192,884.00 E 4,200,850.22 

LCR B-10A 1971 N 4, 192,884.35 E 4,200,850. 15 

Coordinate change 0.36 ft Nl 1-19W 

PACC-2 1966 N 4,216,724.94 E 4, 141 ,566.89 

PAC C-2 1971 N 4,216,726.11 E 4, 141 ,567.46 

Coordinate change 1.30 ft N25-58E 

SYLA-12B 1962 N 4,224,243.46 E 4, 138,271 .47 

SYLA-12B 1971 N 4,224,242. 13 E 4, 138,272.94 

Coordinate change 1 .98 ft S47-52E 

SUNB-2 1964 N 4,217,897.65 E 4, 169,538.46 

SUNB-2 1971 N 4,217,896.01 E 4, 169,533.31 

Coordinate change 5.40 ft S72-20W 

SUNC-3 1940 N 4,213,826.36 E 4, 172,364.82 

SUN C-3 1971 N4, 213, 829. 12 E 4, 172,366.09 

Coordinate change 3.04 ft N24-43E 

SUN H-3 1940 N4, 213, 275. 40 E 4, 185,871 . 12 

SUNH-3 1971 N 4,213,271.28 E 4, 185,871 .96 

Coordinate change 4.20 ft SI 1-31 E 

ZEL L-2 1938 N 4,216,446.85 E 4, 134,280.83 

ZELL-2 1971 N 4,216,447.58 E 4, 134,281 .41 

Coordinate change 0.93 ft N38-28E 



240 San Fernando Earthquake of 1971 



constrained adjustment, based on elevations ol tidal 
bench marks Tidal 8 at Los Angeles Outer Harbor, 
Tidal f> at I. a Jolla, and Tidal 4 A at Point Mugu, as 
well as on six bedrock marks in Ventura, Kern, San 
Bernardino, Riverside, and San Diego Counties, and 
a mark at the County Hall of Justice in the I.os An- 
geles Civic Center. For scientific purposes, a free ad- 
justment also was completed and is available upon 
request. In this latter adjustment, only Tidal 8 was 
held fixed. Several lines of the Coop Net run 
through the area of major earthquake land move- 
ment. 

Following the February 9 earthquake, it was 
agreed that primary vertical control would be rerun 
by the agency that did the work in the Coop Net, 
with LABE being assigned a major role. This con- 
cept was modified when NCS elected to level south- 
ward from Crapevine through Castaic to Pearblos- 
som along Line 205 and leveled Line 207 from 
Palmdale to Rosamond. 

Postearthquake precise leveling was completed as 
shown in figure 5. 

In fully evaluating the results of the releveling as 
they pertain to the San Fernando earthquake, it is 
necessary to take into account subsidence that has 
been occurring in the Los Angeles Basin (including 
the San Fernando Valley) during the past 20-year pe- 
riod in which precise leveling data have been avail- 
able. The apparent movement at BM 5-46C in the 
Wilmington area, showing a continuing history of 
progressive subsidence (table 4) , would not appear 
to be significant with respect to the earthquake; 
however, the movement at BM 60-40, showing an 
uplift after 8 years of downtrend, would appear sig- 
nificant. 



Table 4.— Comparison of elevation changes— subsidence effects 
versus earthquake effects 



Stations 








BM 5^6C 


BM 60-^0 




Locations 
Near intersection of Lomita Boule- San Fernando Road 
vard and Avalon Boulevard in south of Saugus 
Wilmington 


, 0.8 


mile 


Elevations 


Year Elevation Year 




Elevation 



Feet 

1960 43.395 

1964 43.192 

1968 43.071 

1971 *43.008 



1960 


Feet 
1191.899 


1966. . 


1191.710 


1968 


1191.654 


1971 


*1192.06 



* Preliminary only. 



The field data obtained were compiled and 
to NGS foi study and adjustment. All inforn 
on vertical movement shown in tins rc-port is pre- 
liminary. Figure ' shows sc-lccu-d \ertical ' 
in' iiis dc-iiw-d from a comparison of preearthquake- 
constrained 1970 elevations with postearthquake* 
unadjusted preliminar) held elevations. It should be 
noted that only first-order hc-nc h mark locations are 
shown; several ;ne;is ol much greater movement are 
known to exist. 

PARTIV-FINDINGS 

Conclusions 

1 The preearthquake existence of well-monu- 
mented first-order geodetic control, both horizontal 
and vertical, has made possible the collection of a 
significant body of scientific data that will b< 
great value to earth scientists and the engineering 
community. 

2 Published positions of geodetic control stations 
may not form an adequate basis for the scientific 
study of movements resulting from earthquakes. 
Line lengths and directions computed from pub- 
lished positions contain both the accidental errors in- 
herent in direc t measurement and the additional un- 
certainties introduced when the observed data are 
constrained to fit the existing network. 

3 Although both preearthquake- and postearth- 
quake-published positions contain restraints, both 
data sets will be adequate for determining the rela- 
tive positions of points before and after the earth- 
quake and for demonstrating to the courts the dis- 
placements that appear to have occurred. In this 
application of the postearthquake geodetic survey, 
consistency can be expected to be of greater impor- 
tance than ultimate accuracy. 

4 The Southern California Cooperative Leveling 
Program provided an excellent base for the evalua- 
tion of vertical movements resulting from the earth- 
quake. 

5 A local agency coordinated the field 
observation programs of all agencies, resulting in a 
maximum accumulation of data with a minimum of 
duplication of effort. 

6 The availability of electronic distance-measure- 
ment equipment greatly increased the certainty of 
postearthquake positions of the horizontal control 
stations. 






7 Failure to make use of large-scale photogram- 
metric mapping and failure to separate primary hori- 
zontal control from secondary control has delayed 
the publication of final positions and movement data 
by several months. 

8 The delay in publication of final results has, in 
turn, been detrimental to redevelopment of civil 
works in the area. Redevelopment has gone ahead on 
less than the best possible data base. 

9 The low density of control in the San Gabriel 
Mountains area north of San Fernando constituted a 
limitation on the possible movement analysis. 

10 Based on the comparison of preearthquake- 
and postearthquake-constrained values, the greatest 
movement of a first-order horizontal control station 
occurred at station Pacoima L-l, with a movement of 
6.35 feet N.69°W. 

11 Based on the preearthquake-constrained ad- 
justment of the Coop Net and the postearthquake- 
unadjusted preliminary values, the greatest elevation 
change of a precise bench mark was +4.72 feet at 
BM 03-00820 — located near the intersection of Foot- 
hill Boulevard and Hubbard Street. 

12 No significant change appeared in the eleva- 
tion of any bench mark along the CDWR line, 
which generally parallels the San Andreas rift zone; 
hence, it appears that the San Fernando earthquake 
had insignificant, if any, effect in that zone. 

General Recommendations 

1 As future earthquakes occur, a strong local sur- 
vey agency should be selected to coordinate all field 
observation programs and to serve as repository for 
earthquake-related observations and data. 

2 Each governing body should provide emer- 
gency funds for surveying activities and should au- 
thorize its commitment at the lowest responsible 
level in the event of an earthquake. Such funds 
should be available for both direct measurement and 
for photogrammetric mapping. 

3 Local governments should actively encourage 
lateral cooperative surveys so that in time of emer- 
gency the facilities and skills of all technical branches 
can be brought to bear on the problem. 

4 The Federal Government should be encour- 
aged to provide NGS and USGS with additional 
high-accuracy devices and personnel to expedite the 
acquisition and dissemination of geodetic data fol- 
lowing an earthquake. 



Land Movement Studies Related to Earthquake 241 

5 Increased funds should be provided for geo- 
detic programs at all levels in earthquake-prone areas 
so that stress accumulations can be assessed and eval- 
uated later if an earthquake should occur. 

6 The publication of constrained-adjustment 



Table 5.— Index of triangulation stations used with 
figures 9 atul 10 



LACO 


no. Station quad name 


Popular name 


1. ... 


. . . ACR H-3 


. . . Pacifico 


2. ... 


. . . ALT A-5 


. . . Flint 


3 


. . . BPK H-7 


. . . Sawmill 


4 


.. . BURJ-8 


. . . Cahuenga 2 


5 


CAS D-l 


. . . Loma Verde 


6. . .. 


.. . CHA H-6 


. . . Chatsworth 


1 .... 


... DC G-8 


. . . Calabasas 


8 


. . . GV A-10 


. . . Brushy 


9. . . . 


.. . GVC-12 


. . . Deer 


10. .. . 


. . . GV D-9 


. . . House 


11 


.. . LCR C-ll AUX 1 


. . . Verdugo AUX 


12 


. . . LCR H-4 


. . . Sister Elsie 


13. ... 


... LT 1-2 


. . . Port 


14.. . . 


... LTJ-2 




15 






16 






17. .. . 


... NHB-6 


. . . Towsley 


18. . . . 


... NHC-I 


. . . Lock 


19.... 


... NH E-10B 


. . . Ridge 2 


20.... 


... NHH-1 


. . . Newhall 


21.... 


.. . NH H-3 


. . . Edison No. 2 


22.... 


... NH 1-11 


. . . Mission Point 


23.... 


. . . NH J-8 


. . . East 


24. .. . 


.. . PAC B-7 


. . . Darling 


25. ... 


. . . PAC C-l 


. . . Reservoir 1932 


26 


PAC E-2 ECC 1 




27 






28 ... . 


. . . PAC L-5 


. . . Pacoima No. 2 


29. . .. 


. . . PIC L-9 AUX 2 ECC 1 . . . 


San Fernando 
AUX 2 ECC 1 


30 


PIC L-9A. . 




31 


. . . RAV J-5 


. . . Parker 


32 


RAV J-5 AUX 2 


. . . Parker AUX 2 


33... . 


. . . RES K-9 




34 


RES K-9A 




35. . . . 


. . . RR E-10 


. . . Hauser 


36.... 


. . . SAU C-9 


. . . Yucca 


37.... 


. . . SAU D-5 


Long 


38.... 


. . . SAU E-3 


. . . Bum 


39.... 


. . . SAU F-l 


. . . Steer 


40. . .. 


. . . SAU G-8A 


. . . Foot 2 


41 


.. . SAU H-5 


. . . Dry 


42 ... . 


. . . SAU H-l 1 




43 


... SAUJ-2 


. . . View 


44.. .. 


. . . SVC-8 


. . . Pelona 


45 


. . . SV C-8 ECC 2 


. . . Pelona ECC 2 


46 


SYL F-8. 




47. ... 


. . . SYL 1-6 


. . . May 


48 


SYL 1-12 




49 ... . 


. . . WPK A-7A 


. . . Whitaker 


50 


. . . WPK A-7A AUX 1 


. . . Whitaker AUX 1 


51.... 


.. . WPK N-15 


. . . Cast C 


52 ... . 


... WSM B-13 




53 


.. . WSM C-10 


. . . Daires 


54. . . . 


. . . WSM F-4 


. . . Warm Springs 


55. .. . 


.. . WSM F-6 


. . . Necktie 


56 ... . 


... WSM F-13 A 


. . . Charlie 


57... . 


... WSM H-10 


. . . Taylor 


58. .. . 


.. . WSM J-8 


. . . Elizabeth 


59. . .. 


. . . WSM K-ll 




60. .. . 


. . . WSM M-5 


. . . Red 1932 


61 


.. . WSM N-13 


. . . Rock 


62 ... . 


. ... ZEL H-2 


. . . Bluff 


63. ... 


. . . . ZEL I-6D 


. . . Corner 2 


64 




. . . Mays 2 


65 




. . . Mpsa 





242 San Fernando Earthquake of 1971 



positions should he- continued lor engineering usage, 
but all such data should be dated and be considered 
incomplete without such a date. 

Specific Recommendations 

Relative to the 1971 San Fernando earthquake, it 
is recommended that: 

1 All survey data developed by local agencies 
pertinent to the event should continue to be submit- 
ted to LACO for filing and general access. 

2 Planning meetings should be scheduled to 
prepare the releveling needs for the Southern Cali- 
fornia Cooperative Leveling Program in keeping 
with the 1968 plan. 

ACKNOWLEDGMENTS 

This report was prepared for the NOAA/EERI 
Subcommittee on Geodesy. Members of the commit- 
tee were: 

Chairman 

Ira H. Alexander, Assistant Chief Deputy County Engi 

neer, Department of County Engineer, County of Los 

Angeles. 

John A. Lambie, County Engineer, Department of County 

Engineer, County of Los Angeles (until March 31, 

1971). 

Harvey T. Brandt, County Engineer, Department of 

County Engineer, County of Los Angeles. 
George J. Franceschini, Division Engineer, Survey Divi- 
sion, Department of County Engineer, County of Los 
Angeles. 
Richard J. Mitchell, Assistant Division Engineer, Survey 
Division, Department of County Engineer, County of 
Los Angeles. 
John F. McMillan, Head, Geodetic Section — Survey Divi- 
sion, Department of County Engineer, County of Los 
Angeles. 
Henry Beitler, Chief of Surveys, Los Angeles City Bureau 
of Engineering. 



Organizations and agencies thai most helpful 

in providing data, and field and other assistance, are 
listed in Part I Work Resume of Agencies The 
subcommittee gratefully acknowledges the "junsel 
and assistance given them by Charles Whitten 
ard Baker, liuford Meade, Roy Williamson, and Jo- 
seph I)ia( up of the National Geodetic Survey. 

REFERENCES 

Anonymous, "Aerospace Charting and Geodetic S<-r\ ." Cali- 
fornia Earthquake Area," The Military Engineer, Vol. 63, 
No. 415, Sept.-Oct. 1971, p. 353. 

Franceschini, G. J., and Mitchell, R. ]. ('Survey Division Dept. 
of Los Angeles County Engineer, Los Angeles Calif.), 
"Southern California Cooperative Leveling Program," paper 
presented at the 29th annual meeting of the Ami 
Congress on Surveying and Mapping. Washington, D.C, 
Mar. 9-14, 1969. 

Los Angeles County Earthquake Commission, San Fernando 
Earthquake, February 9, 1971 , Los Angeles, Calif., Nov. 1971, 
45 pp. 

Savage, James C, Burford, R. O., and Kinoshita, W. T., 
Earth Movements From Geodetic Measurements, U.S. Geo- 
logical Survey, National Center for Earthquake R< search, 
Menlo Park, Calif., Jan. 1972, 41 pp. (unpublished manu- 
script) . 

U.S. Coast and Geodetic Survey, "First and Second Order Tri- 
angulation in California (1927 Datum) ," Special Publication 
202, U.S. Department of Commerce, Washington, D.C, 1936, 
548 pp. 

U.S. Coast and Geodetic Survey, "The State Coordinate System 
(a Manual for Surveyors) ," Special Publication 235, U.S. 
Department of Commerce, Washington, D.C, 1945, 62 pp. 

U.S. Coast and Geodetic Survey, "Definitions of Terms Used 
in Geodetic and Other Surveys," Special Publication 242, 
U.S. Department of Commerce, Washington, D.C, 1948, 
87 pp. 

U.S. Coast and Geodetic Survey, "Manual of Geodetic Trian- 
gulation," Special Publication 247. U.S. Department of Com- 
merce, Washington, D.C, 1950. 344 pp. 

U.S. Coast and Geodetic Survey, "Plane Coordinate Projection 
Tables — California (Lambert) ," Special Publication 253, 
U.S. Department of Commerce, Washington, D.C, 1951, 
70 pp. 



Horizontal Crustal Movements 
Determined From Surveys 
After San Fernando Earthquake 



CONTENTS 


Page 




243 


Introduction 


243 


Preearthquake Triangulation 


244 


POSTEARTHQUAKE TRIANCULATION AND 




Trilateration 


247 


Adjustments and Results 


248 


Adjustment 1 


251 


Adjustment 2 


251 


Adjustment 3 


251 


Conclusions 


254 


References 



BUFORD K. MEADE 
ROBERT W. MILLER 

National Geodetic Survey 
National Ocean Survey, NOAA 



INTRODUCTION 

Horizontal control surveys from 1922 to 1967 were 
combined into a single composite network for use as 
a preearthquake survey and compared with the re- 
sults of surveys made soon after the February 9, 
1971, earthquake. This net in Los Angeles County is 
bounded approximately by latitude 34°08' to 34°42' 
N. and longitude 118°02' to 118°45' W. Tables 1A 
and IB list the stations and their respective code 
numbers used in the preearthquake and postearth- 
quake survey solutions. 

Before the earthquake, a field party from the Na- 
tional Oceanic and Atmospheric Administration's 
(NOAA) National Ocean Survey was engaged in a 
resurvey of Barrel, a small triangulation net, which 
had been established along the route of the Califor- 
nia Aqueduct. After the earthquake, two sites — Bar- 
rel (35 km northeast of the epicenter) and Cast (25 
km northwest of the epicenter) — were resurveyed to 
detect possible fault slippage. At the Barrel site, the 
results of surveys just before and following the earth- 
quake did not show any significant differences. Also, 
these results were in close agreement with previous 
surveys of 1964, 1965, 1966, and 1967. At the Cast 
site, the overall change from 1964 to 1971 indicates 
possible right-lateral movement of a few millimeters, 
although in 1971 it was determined that this net- 
work did not straddle the San Gabriel fault. 

PREEARTHQUAKE TRIANGULATION 

Some of the triangulation stations used in the 
preearthquake composite network had been used in 
previous crustal movement studies. The stations used 
in this investigation are listed in table 1C, together 



243 



244 San Fernando Earthquake of 1971 
Summary Key to Tables 

Pagi 
HORIZONTAL CONTROL STATIONS 

Preearthquake station indexes: Tabic 1A 245 

POSTEARTHQUAKE STATION INDEXES! Tabic IB 240 

Common preearthquake and postearthquake 
stations: Table 1C 247 

PREEARTHQUAKE TRIANCULATION 

Observed horizontal directions: Tabic 2A 249 

Measured lengths: Tabic 2B 250 

POSTEARTHQUAKE TRIANCULATION AND 
TRILATERATION 

Observed horizontal directions: Tabic 3A 253 

Measured lengths: Table 3B 255 

Azimuth control: Table 4A '^ r >'> 

Triangle closures: Table 4B 256 

Elevations of stations: Tabic 4C 256 

ADJUSTMENTS AND RESULTS 

Adjustment 1 

Corrections to directions: 

Preearthquake: Table 5A 257 

Postearthquake: Table 5B 259 

Corrections to lengths: 

Preearthquake: Table 6A 260 

Postearthquake: Table 6B 261 

Adjusted geographic positions: 

Preearthquake: Table 7A 263 

Postearthquake: Table 7B 264 

Position shifts: Table 8A 265 

Error ellipses: Table 9A 266 

Parameters of strain: Table 10 268 

Adjustment 2 

Corrections to directions: 

Preearthquake: Table 5C 273 

Postearthquake: Table 5D 275 

Corrections to lengths: 

Preearthquake: Table 6C 276 

Postearthquake: Table 6D 277 

Adjusted geographic positions: 

Preearthquake: Table 7C 279 

Postearthquake: Table 7D 280 

Position shifts: Table 8B 281 

Adjustment 3 

Corrections to directions: 

Preearthquake: Table 5E 283 

Postearthquake: Table 5F 285 

Corrections to lengths: 

Preearthquake: Table 6E 286 

Postearthquake: Table 6F 287 

Adjusted geographic positions: 

Preearthquake: Table 7E 289 

Postearthquake: Table 7F 290 

Position shifts: Table 8C 291 

Error ellipses: Table 9B 292 



with the dati tations i er< • tablished and the 

dates of the survey observations used in the adjust- 
ment. I his network is shown in figure IA. 

The combined fust order horizontal d 
used in the preearthquake adjustment are listed in 
table 2A. 

Six of the lines in the preearthquake network had 
been measured with the Geodimeter. Two other dis- 
tances, previously determiner! in an adjustment of 
the Los Angeles City (LAC) net, were used with the 
six Geodimetei distances to provide length control. 
These values are listed in table 2B. 

POSTEARTHQUAKE TRIANCULATION AND 
TRILATERATION 

Shortly after the earthquake, a resurvey was made 
to measure earth movement. It was a cooperative ef- 
fort by personnel of the National Ocean Survey 

(NOS) , the Los Angeles County Engineer (LACE), 
and the Los Angeles City Bureau of Engineering 

(LACBE) , using first-order class-I specifications. 

This network ol stations is shown in figure IB. 

Observations made by LACE and LACBE and in- 
corporated in the postearthquake adjustments are as 
follows: 



LACE 




LACBE 


station numbers 




station 








numbers 


701 717 


729 


746 


706 


702 720 


732 


747 


718 


703 724 


736 


752 


719 


707 726 


737 


766 


721 


715 727 


738 







Four stations that could not be recovered or found 
were replaced by the following stations: Foot 2, Pa- 
coima E-2 ECC 1, Ridge 2, and Verdugo AUX. 

All observations used in these adjustments were 
made after the February 9, 1971, earthquake except 
for station Rock (751), observed in July 1963, and 
stations Cast (760) , Fork (761) , and Necktie (763), 
observed in July 1964. These four stations, near the 
northern edge of the project, were included to 
strengthen the net. Postearthquake observations at 
adjacent stations were in very close agreement with 
the preearthquake values, and these observational 
checks indicated there were no significant move- 
ments in this area. 



The following seven auxiliary new stations were 
ied to previously established stations by distance 
md direction: 



Station number 



'06. 
'20. 
'26. 
'33. 



Station name 
Pacoima E-2 ECC 1 (Aqueduct #1 ECC 1) 
MTW E-10A 
Parker AUX 2 
Pelona ECC 2 



Horizontal Crustal Movements 245 

Station number Station name 

736 Pico L-9A 

737 Pico L-9 AUX 2 ECC 1 (San Fernando 

AUX 2 ECC 1). 
766 WPKA-7AAUX1 

The postearthquake horizontal directions are 
listed in table 3A. At the following eight stations, 
horizontal directions observed by NOS and LAC 



Table 1 A. —Numerical and alphabetical indexes of stations used in preearthquake survey 



itation no. Numerical station name 

K31 Calabasas USGS LAC&C 

X)2 San Vicente No. 1 LA WD LAC&C 

■03 Chatsworth USGS LAC&C 

m Sylmar F-8 LAC 

X35 Pacoima L-l LAC 

)06 Aqueduct No. 1 Pacoima E-2 LAC 

307 Sylmar 1-12 LAC 

308 Sylmar 1-9 LAC 

)09 Reservoir 

)10 Corner 2 

111 Bluff 

)12 Mission Pt. 

313 Ridge 

)14 Darling USGS LAC&C 

)15 Pacoima No. 2 LAC&C 

316 Fernando 2 USGS LAC&C 

317 Cahuenga 2 LAC 

318 Verdugo USGS LAC&C 

319 Flint LA WD LAC&C 

320 Wilson Peak 

321 Sister Elsie USGS LAC&C 

322 Iron 

323 Gleason 

324 Pacifico 

325 Pacifico 

326 Vince 

327 Mt. Gleason LAC 

328 Tenhi 

329 Hauser 

330 Parker 

331 Magic 

332 Port Little Tujunga 1-2 LAC 

333 Pelona ECC 2 LAC 

334 Pelona 

335 Jupiter Mt. USGS 

336 Bee 

337 Surge 

338 House 

339 Red 

340 Brushy 

341 Powerhouse 

342 Rock 

343 Steer 

344 View 

345 Bum 

346 Dry 

347 Long 

'348 Foot 

349 Yucca 

050 Saugus 

051 Lock 

052 Newhall 

053 Towsley 

054 East 

055 Edison 

056 May 

057 San Fernando 

058 Pico L-9 AUX 2 ECC 1 S F AUX 2 ECC 1 LAC 

059 Deer USGS Green Valley C- 12 LAC 

060 Loma Verde USGS LAC 

061 WPK A-7A AUX 1 Whitaker LOT AUX 1 LAC 

062 Whitaker 

063 Warm Springs 

064 Sawmill 



Station no. 



Alphabetical station name 



006 Aqueduct No. 1 Pacoima E-2 LAC 

036 Bee 

Oil Bluff 

040 Brushy 

045 Bum 

017 Cahuenga 2 LAC 

001 Calabasas USGS LAC&C 

003 Chatsworth USGS LAC&C 

010 Corner 2 

014 Darling USGS LAC&C 

059 Deer USGS Green Valley C- 12 LAC 

046 Dry 

054 East 

055 Edison 

016 Fernando 2 USGS LAC&C 

019 Flint LAWD LAC&C 

048 Foot 

023 Gleason 

029 Hauser 

038 House 

022 Iron 

035 Jupiter Mt. USGS 

051 Lock 

060 Loma Verde USGS LAC 

047 Long 

031 Magic 

056 May 

012 Mission Pt. 

027 Mt. Gleason LAC 

052 Newhall 

024 Pacifico 

025 Pacifico 

005 Pacoima L-l LAC 

015 Pacoima No. 2 LAC&C 

030 Parker 

034 Pelona 

033 Pelona ECC 2 LAC 

058 Pico L-9 AUX 2 ECC 1 S F AUX 2 ECC 1 LAC 

032 Port Little Tujunga 1-2 LAC 

041 Powerhouse 

039 Red 

009 Reservoir 

013 Ridge 

042 Rock 

057 San Fernando 

002 San Vicente No. 1 LAWD LAC&C 

050 Saugus 

064 Sawmill 

021 Sister Elsie USGS LAC&C 

043 Steer 

037 Surge 

004 Sylmar F-8 LAC 

008 Sylmar 1-9 LAC 

007 Sylmar 1-12 LAC 

028 Tenhi 

053 Towsley 

018 Verdugo USGS LAC&C 

044 View 

026 Vince 

063 Warm Springs 

062 Whitaker 

020 Wilson Peak 

061 WPK A-7A AUX 1 Whitaker LOT AUX 1 LAC 

049 Yucca 



246 



San Fernando Earthquake of 1 97 J 



Table IB.— Numerical and alphabetical mdexet «/ nation* "W m potUarthquakt %unry 



Station no. 



Niiiikik .il itation name 



Station no 



Alp). 



701 Calabasas USGS !.A< I 

702 RES K. <)A LAC 

703 Chataworth USGS LAC&C 

704 Sylmar F» I.AC 

705 Pacoima L 1 I.AC 

706 PAC E-2 ECC 1 I.AC 

707 Sylmar 1-12 LAC 

709 Reservoir 

710 Corner 2 

711 Bluff 

712 Mission Pt. 

713 Ridge 2 

715 Pacoima No. 2 LAC&C 

717 Cahuenga 2 LAC 

718 Verdugo AUX I.AC 

719 Flint LAWD LAC&C 

720 MTW E-10A LAC 

721 Sister Elsie USGS LAC&C 

724 Pacifico 

726 Parker AUX 2 LAC 

727 Mt. Gleason LAC 

729 Hauser 

730 Parker 

731 Magic 

732 Port Little Tujunga 1-2 LAC 

733 Pelona ECC 2 LAC 

734 Pelona 

735 East 

736 Pico L-9A LAC 

737 Pico L-9 AUX 2 ECC 1 S F AUX 2 ECC 1 LAC 

738 May 

739 Edison 

740 Towsley 

741 Newhall 

742 Lock 

743 Saugus 

744 Yucca 

745 Foot 2 

746 Long 

747 Dry 

748 Bum 

749 View 

750 Steer 

751 Rock 

752 Deer USGS Green Valley C-12 LAC 

753 House 

754 Brushy 

755 Red 

756 Powerhouse 

757 Charlie 

758 Taylor 

759 Elizabeth 

760 Cast C 

761 Fork CDWR 

762 Daires 

763 Necktie 

764 Loma Verde USGS LAC 

765 Whitaker 

766 WPK A-7A AUX 1 Whitaker LOT AUX 1 LAC 

767 Warm Springs 

768 Sawmill 



711 Bluff 

/ A Bnifhy 

748 Burn 

717 . Cahuenga 2 I.AC 

701 Calabatai ' SGS L.V 

760 ' 

757 Charlie 

703 Chattworth USGS I ' ' 

710 Cornei 2 

762 Daires 

702 Deei i 5GS Green Valley C 12 LAC 
747 Dry 

735 I 

7 ',') Edison 

7 r /» Elizabeth 

719 I Imt LAWD LAI 

745 Foot 2 

761 I ork CDWR 
729 Hauser 

753 li 

742 Lock 

Loma Verde USGS LAC 

746 Long 

731 Magic 

738 May 

712 Mission Pt. 

727 Mt. Gleason LAC 

720 MTW B-10A LAC 

763 Necktie 

741 Newhall 

706 PAC I- 2 ECC 1 LAC 

724 Pacifico 

705 Pacoima L-l LAC 

715 Pacoima No. 2 LAC&C 

730 Parker 

726 Parker AUX 2 LAC 

734 Pelona 

733 Pelona ECC 2 LAC 

737 Pico L-9 AUX 2 ECC 1 S F AUX 2 ECC 1 LAC 

736 Pico L-9A LAC 

732 Port Little Tujunga 1-2 LAC 

756 Powerhouse 

755 Red 

702 RES K-9A LAC 

709 Reservoir 

713 Ridge 2 

751 Rock 

743 Saugus 

768 Sawmill 

721 Sister Elsie USGS LAC&C 

750 Steer 

704 SvlmarF-8LAC 

707 Svlmar 1-12 LAC 

758 Taylor 

740 Towsley 

718 Verdugo AUX LAC 

749 View 

767 Warm Springs 

765 Whitaker 

766 WPK A-7A AUX 1 Whitaker LOT AUX 1 LAC 

744 Yucca 



were combined and used in the adjustments: Hauser 
(729) , Port (732) , Pico L-9 AUX 2 ECC 1 (737) , 
May (738), Long (746), Dry (747), Deer (752), 
and WPK A-7A AUX 1 (766) . 

A very large percentage of the lines in the post- 
earthquake survey was measured with the Geodime- 
ter. Most of these distances were measured by NOS, 
with some assistance by LACE, using a laser-type 



Geodimeter. Twenty-two of the distances were meas- 
ured by LAC and two by the U.S. Geological Survey 
(USGS) . The two L T SGS distances were taken from 
a preliminary report (Savage 1971). These were in- 
cluded to obtain a postearthquake position for sta- 
tion Sylmar 1-12 (707). All of the measured dis- 
tances are listed in table 3B. 

Other observational and statistical data used in the 



Horizontal Crustal Movements 



247 



Table lC.—Preearthquake network of stations used in 
post earthquake investigation 



Station 
number 



Station name 



1 *Calabasas 

2 *San Vicente No. 1 . 

3 *Chatsworth 

4 *Sylmar F-8 

5 *Pacoima L-l 



6 *Aqueduct No. 1 . 

7 *Sylmar 1-12. . . 

8 *Sylmar 1-9 

9 Reservoir 

10 Corner 2 



11 Bluff 

12 Mission Pt.. . 

13 Ridge 

14 *Darling 

15 *Pacoima No. 

16 *Fernando 2.. 

17 *Cahuenga 2. 

18 *Verdugo . . . . 

19 *Flint 

20 Wilson Peak. 



21 *Sister Elsie. 

22 Iron 

23 Gleason... 

24 Pacifico. . . 

25 Pacifico. . . 



26 Vince 

27 *Mt. Gleason. 

28 Tenhi 

29 Hauser 

30 Parker 



31 Magic 

32 *Port 

33 *Pelona ECC 2. 

34 Pelona 

35 Jupiter Mt . . . 

36 Bee 

37 Surge 

38 House 

39 Red 

40 Brushy 



41 Powerhouse . 

42 Rock 

43 Steer 

44 View 

45 Bum 

46 Dry 

47 Long 

'48 Foot 

49 Yucca 

50 Saugus 



51 Lock 

52 Newhall. 

53 Towsley. . 

54 East 

55 Edison . . . 



56 May 

57 San Fernando 

58 *Pico L-9 AUX 2 ECC 1 

59 *Deer 

60 Loma Verde 



61 *WPK A-7A AUX 1 

62 Whitaker 

63 Warm Springs 

64 Sawmill 



Year 
established 



Year of 

survey 

used 



1933 
1933 
1933 
1935 
1935 



1934 
1934 
1934 
1936 
1936 



1924 


1936, 1955 


1936 


1936 


1936 


1936 


1932 


1932-63 


1963 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1933 


1934, 1936 


1933 


1934-55 


1933 


1934, 1955 


1933 


1934 


1933 


1934, 1958 


1933 


1934 


1890 


1934, 1958 


1933 


1934, 1958 


1958 


1958 


1958 


1958 


1958 


1958 


1958 


1964 


1938 


1940, 1958 


1965 


1965 


1938 


1938-64 


1938 


1938-65 


1940 


1940-65 


1958 


1958 


1964 


1964 


1961 


1965 


1932 


1932-67 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1932-64 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1963 


1932 


1932-64 


1898 


1922-65 


1961 


1964-65 


1964 


1964-65 


1932 


1932-67 


1964 


1964 


1941 


1941-65 


1941 


1941-65 


1932 


1932-67 



* Station established by LAC. 



investigation are listed in tables 4A, 4B, and 4C, as 
follows: 

Table 4A — lines used for azimuth control; 

Table 4B — average and maximum triangle closures of the pre- 

earthquake and postearthquake surveys; and 
Table 4C — elevations of stations used in reduction of Geodimeter 

distances. 

ADJUSTMENTS AND RESULTS 

In an attempt to obtain a geometrical representa- 
tion of horizontal crustal movement in the region, 
several hypotheses based on physical and geological 
evidence may be assumed. In this study, three as- 
sumptions were made and tested with the same ob- 
servational data. The first assumption (adjustment 
1) provided for the possibility that all stations, ex- 
cept one station used for position control, may shift. 
The second assumption (adjustment 2) hypothesized 
that stations along the outer rim of the net have not 
moved between surveys. The third assumption (ad- 
justment 3) relaxed the condition of no movement 
along the western side of the project at stations Chats- 
worth, San Fernando, Pico L-9 AUX 2 ECC 1, and 
Pico L-9A. The same observational data were used 
for each of the three adjustments. The only varia- 
tions were the constraints on positions. All adjust- 
ments were referenced to the North American 
Datum of 1927. 

Unit weight, based on a standard error of 0."5, was 
assigned to each direction and azimuth observation. 
Weights for the Geodimeter measurements were 
based on the following equation for standard error, 

standard error = 0.006 m + 1 ppm + 5 / 3 AH X 1 s , 

where AH is the difference in elevation between ter- 
minals of the line. 

Unit weight for the distance observations, equiva- 
lent to 0."5 for the direction observations, is then a 
standard error of one part in 412,000 of the distance. 

In the adjustment procedure used, that is, by vari- 
ation of geographic coordinates, observation equa- 
tions were formed for each direction, azimuth, and 
length observation. These observation equations 
were then multiplied by a factor proportional to the 
a priori value of the standard error of unit weight. 
In some of the tabulated results, these multipliers 
are identified as weight factors. 

The standard error of an observation of unit 
weight, as obtained from the adjustments, was in 
very close agreement with the a priori value assigned. 



248 



San Fernando Earthquake of 1971 



•;.:> 




. 



- 






• 



-->.- 



Figure 1A. — Preearthquake triangulation net (1922-1967). 



Adjustment 1 

A free adjustment (the network is not constrained 
to fit previously adjusted geographic positions) was 
made using the least-squares variation of geographic 
coordinates method and all of the combined 
preearthquake observations. Another free adjustment 
was made using the postearthquake observations. 
Only one position, station Cahuenga 2, was held 



fixed. Variance-covariance matrices were computed 
to determine error ellipses for stations common to 
the two surveys. 

Results 

The corrections applied to the horizontal direc- 
tions are given in table 5A for the preearthquake 
survey and in table 5B for the postearthquake sur- 



Horizontal Crustal Movements 



249 



Table 2A.—Preearthquake observed horizontal directions 



Table 2A.—Preearthquake observed horizontal directions— Continued 



Station 



From 



To 



Observed 
direction 



Station 



From 



To 



Observed 
direction 



Station 



From 



To 



Observed 
direction 



Station 



From 



To 



Observed 
direction 



001 



003 


000 00 00.00 


057 


009 00 15.80 


014 


048 52 51.96 


002 


093 46 46.23 


001 


000 00 00.00 


003 


044 32 19.54 


057 


064 07 1 1 . 78 


014 


093 44 51.68 


016 


103 32 45.31 


015 


116 51 26.86 


018 


149 57 51.64 


017 


170 59 43.51 


057 


000 00 00.00 


016 


038 10 59.29 


014 


070 49 05.72 


002 


116 02 26.78 


001 


157 43 22.02 


008 


000 00 00.00 


005 


015 11 34.25 


007 


028 11 46.00 


015 


029 32 05.45 


006 


064 12 02.77 


015 


000 00 00.00 


014 


052 22 46.86 


006 


082 51 46.45 


007 


116 17 32.28 


004 


134 41 16.31 


008 


143 39 30.46 


004 


000 00 00.00 


056 


016 26 42.22 


016 


023 25 33.60 


008 


028 23 16.13 


007 


048 55 20.10 


005 


079 10 01.69 


015 


113 08 46.69 


014 


199 58 42.72 


009 


269 07 22.81 


004 


000 00 00.00 


008 


033 41 13.54 


005 


148 36 02.53 


006 


264 55 34.59 


005 


000 00 00.00 


007 


037 43 13.25 


006 


068 25 30.48 


004 


155 50 11.61 


012 


000 00 00.00 


056 


100 51 42.26 


010 


280 26 26.50 


011 


326 26 57.38 


016 


105 47 59.00 


006 


158 04 04.37 


015 


175 02 41.87 


011 


000 00 00.00 


012 


018 03 58.14 


009 


067 54 04 . 1 1 


057 


359 52 07.78 


013 


017 18 26.78 


012 


062 55 41.96 


056 


104 21 06.86 


009 


133 48 49.78 


010 


199 54 13.41 


056 


000 00 00.00 


009 


053 01 24.17 



012 



013 



014 



015 



016 



017 



018 



019 



020 







020 


010 


103 37 44.08 




011 


128 35 14.18 


021 


013 


222 55 50.33 




054 


313 43 12.75 




057 


359 38 19.63 




054 


128 47 34.72 




012 


179 16 20.54 




011 


219 18 28.08 




057 


000 00 00.00 




006 


074 39 49.14 




016 


076 44 07.99 


022 


005 


103 22 08.58 




015 


122 48 30.00 




017 


176 29 45.86 




002 


237 29 32.20 


023 


001 


278 50 48.31 




003 


323 03 40.59 




016 


359 59 59.79 




005 


007 55 24.28 




021 


092 26 32.89 




018 


119 06 15.73 




017 


156 15 16.05 


024 


002 


217 32 08.07 


014 


259 44 32.29 




057 


297 16 19.94 




009 


297 43 09.19 




006 


304 45 55.69 


025 


004 


336 57 11.75 




056 


353 28 46.25 




021 


000 00 00.00 


026 


018 


020 49 38.78 




017 


041 01 03.77 




015 


055 39 52.49 




002 


079 53 19.91 




014 


089 20 03.85 


027 


006 


090 42 35.08 




009 


104 08 19.07 




003 


123 01 27.55 




057 


141 41 06.99 




056 


144 46 35.82 




002 


000 00 00.00 


028 


014 


041 45 24.00 




015 


064 34 53.69 




016 


073 40 48.81 




018 


118 58 01.01 


029 


021 


121 37 31.54 




020 


161 21 15.56 




019 


169 02 19.43 




021 


000 00 00.00 




020 


054 55 59.30 




019 


094 23 35.89 


030 


017 


173 42 45.12 




002 


213 42 56.14 




015 


262 10 38.87 




056 


285 35 44.25 




016 


288 14 08.69 




017 


000 00 00.00 




018 


050 36 32.14 




021 


085 28 58.48 




020 


165 39 02.69 


031 


018 


359 59 59.80 




057 


016 08 03.33 




021 


019 47 10.14 




023 


060 46 42.20 




024 


100 44 06.65 




019 


334 30 04.40 





032 



017 


341 09 


59.64 


018 


359 59 


59.66 


015 


055 30 


56.65 


056 


085 30 


31.39 


016 


087 24 


31.63 


031 


118 23 


37.07 


022 


153 31 


29.11 


023 


173 58 


30.28 


020 


254 43 


08.62 


019 


309 16 


00.75 


017 


356 22 


16.27 


023 


000 00 


00.00 


021 


126 55 


03.80 


031 


237 58 


28.76 


022 


000 00 


00.00 


031 


036 14 


05.91 


030 


098 01 


03.55 


026 


146 54 


00.71 


024 


207 54 


26.94 


020 


269 06 


16.08 


021 


327 22 


05.24 


020 


000 00 


00.00 


023 


078 50 


47.92 


026 


147 02 


31.61 


027 


000 00 


00.00 


029 


045 36 


24.97 


028 


055 22 


36.63 


023 


042 55 


39.31 


030 


083 42 


20.08 


034 


122 49 


59.40 


024 


352 07 


51.08 


032 


000 00 


00.00 


033 


051 00 


32.71 


030 


069 03 


14.31 


029 


081 11 


27.90 


028 


102 04 


14.50 


025 


182 26 


54.95 


027 


155 01 


10.59 


030 


182 40 


30.20 


029 


250 10 


09.04 


028 


176 55 


10.43 


025 


207 45 


19.59 


027 


240 53 


26.67 


030 


251 40 


12.40 


032 


280 19 


37.34 


033 


346 15 


21.00 


026 


000 00 


00.00 


023 


090 20 


20.03 


027 


092 14 


05.02 


031 


161 40 


27.28 


032 


164 48 


21.74 


033 


245 00 


16.48 


034 


245 07 


00.98 


029 


295 09 


04.84 


028 


332 54 


24.91 


034 


000 00 


00.00 


030 


058 20 


35.25 


023 


105 13 


31.12 


022 


126 57 


51 .46 


021 


160 46 


37.53 


056 


259 56 


38.95 


032 


281 08 


09.30 



033 



034 



035 



036 



037 



038 



039 



040 



041 



042 



056 


000 


00 


00 


00 


059 


072 


15 


00 


46 


033 


105 


16 


03 


75 


029 


142 


43 


21 


28 


030 


163 


43 


14 


40 


027 


202 


05 


41 


92 


031 


203 


22 


49 


23 


029 


000 


00 


00 


.00 


030 


035 


16 


03 


13 


027 


044 


27 


08 


.73 


032 


076 


36 


57 


79 


056 


100 


03 


53 


66 


059 


158 


20 


36 


08 


026 


062 


21 


59 


16 


030 


088 


21 


20 


75 


031 


126 


34 


11 


65 


056 


152 


59 


46 


02 


060 


212 


46 


06 


92 


036 


234 


04 


38 


10 


039 


237 


13 


02 


76 


064 


264 


40 


31 


46 


035 


274 


50 


40 


28 


036 


000 


00 


00 


00 


038 


034 


04 


14 


97 


039 


062 


22 


15 


18 


037 


068 


02 


30 


38 


064 


104 


15 


51 


66 


034 


297 


38 


21 


94 


038 


000 


00 


00 


00 


037 


055 


11 


23 


39 


035 


122 


30 


17 


75 


034 


199 


22 


36 


54 


039 


000 


00 


00 


00 


035 


190 


02 


26 


70 


036 


234 


41 


01 


21 


038 


300 


40 


29 


20 


040 


317 


39 


32 


72 


039 


000 


00 


00 


00 


037 


074 


48 


02 


35 


035 


110 


11 


44 


10 


036 


133 


37 


09 


30 


040 


300 


49 


39 


85 


064 


000 


00 


00 


00 


037 


094 


40 


32 


57 


035 


099 


02 


43 


10 


034 


116 


41 


11 


48 


038 


140 


32 


59 


48 


040 


170 


41 


29 


86 


056 


177 


50 


25 


32 


042 


190 


37 


08 


86 


041 


209 


41 


12 


52 


060 


249 


20 


58 


04 


063 


297 


14 


06 


92 


042 


000 


00 


00 


00 


041 


045 


04 


48 


51 


039 


129 


58 


13 


33 


037 


191 


36 


47 


49 


038 


220 


39 


21 


73 


043 


000 


00 


00 


00 


039 


177 


37 


22 


46 


040 


233 


44 


15 


88 


042 


293 


42 


23 


25 


044 


322 


24 


48. 


76 


044 


000 


00 


00. 


00 



250 



San Fernando Earthquake of 1971 



Table 2A.— Preearthquake obiewed horizontal directions— Continued Table 2A.— Preearthquake observed horiumUd diret don: -Cot 



Station 



From 



To 



Observed 
direction 



Station 



From 



042 



043 



044 



045 



046 



047 



048 



049 



050 



051 



052 



053 



043 


050 35 


52.96 


041 


123 39 


14.97 


039 


168 30 


08.99 


040 


198 36 


18.13 


045 


000 00 


on do 


041 


161 17 


1 7 . 70 


042 


201 56 


19.18 


044 


248 51 


20.02 


046 


311 49 


13.58 


046 


000 00 


00 00 


045 


040 20 


47.59 


043 


070 48 


37.69 


041 


125 39 


25 . 27 


042 


153 17 


43.61 


047 


000 00 


00.00 


043 


193 50 


12.84 


044 


232 13 


44.11 


046 


287 06 


46.88 


048 


314 08 


34.01 


048 


000 00 


00.00 


047 


088 47 


29.92 


045 


123 35 


03.13 


043 


162 07 


42.38 


044 


208 21 


11.14 


049 


000 00 


00.00 


045 


190 45 


24.95 


046 


263 04 


38.29 


048 


306 20 


56.70 


050 


320 02 


20.64 


050 


000 00 


00.00 


049 


081 54 


31.96 


047 


142 34 


26.78 


045 


161 07 


29.87 


046 


190 30 


38.97 


047 


000 00 


00.00 


048 


065 41 


01.91 


050 


101 41 


21.25 


056 


111 47 


02.90 


052 


123 31 


56.78 


051 


173 21 


07.87 


052 


000 00 


00.00 


051 


067 40 


16.00 


049 


121 20 


34.27 


047 


159 41 


35.64 


048 


183 25 44.06 


049 


000 00 


00.00 


050 


054 39 


54.19 


052 


086 25 


43.37 


055 


112 27 


50.46 


053 


186 24 


13.32 


055 


000 00 


00.00 


057 


038 37 


22.86 


053 


048 48 


09.06 


051 


088 13 


23.93 


049 


131 58 


28.50 


050 


168 47 


19.54 


056 


294 02 


53 . 35 


054 


344 36 


22.41 


051 


000 00 


00.00 


052 


040 36 


15.08 


055 


057 27 


09.46 


054 


091 50 


59.54 


057 


187 56 


44.57 



054 



055 



056 



057 



058 



059 



To 



■ i ved 
diM i lion 



060 



056 


000 00 


00 00 


012 


114 40 


2i, 08 


013 


153 24 


17.65 


057 


173 52 


28.47 


(IV, 


197 35 


4 1 29 


055 




43 80 


052 


262 09 


08.20 


054 


000 00 


00.00 


057 


072 19 


53 . 40 


053 


089 40 


07 28 


051 


138 16 


35.60 


052 


204 01 


03.40 


034 


359 59 


59.92 


033 


000 02 


41 55 


032 


051 19 


41 .80 


031 


ov, 31 


05 ;;i 


016 


oi.« on 


32 58 


021 


101 27 


57.96 


018 


121 33 


09.92 


015 


152 30 


33.81 


006 


187 05 


39.37 


009 


202 33 


59 32 


011 


218 41 


32.64 


012 


228 40 


52.10 


057 


244 49 


49.64 


058 


245 06 


10.17 


054 


247 43 


39.78 


052 


279 19 


17.31 


060 


289 50 


55.22 


061 


293 31 


1 1 . 34 


039 


325 22 


30.75 


064 


326 02 


41 .53 


059 


331 03 


04.16 


062 


121 31 


44.70 


060 


129 11 


52.73 


053 


165 21 


17.34 


059 


174 18 


54.59 


052 


187 50 


00.20 


055 


197 31 


28.54 


054 


225 32 


20.64 


016 


228 59 


17.34 


056 


228 46 


03.10 


020 


250 57 


42.51 


013 


255 54 


55.98 


015 


260 14 


23.69 


011 


278 08 


45.37 


014 


279 54 


05.61 


002 


307 45 


57.40 


001 


338 52 


18.06 


003 


352 08 


37.84 


061 


000 00 


00.00 


063 


030 06 


41.27 


059 


052 55 


49.69 


056 


107 33 


30.37 


058 


000 05 


46.26 


061 


072 33 


33.86 


063 


100 25 


53.15 


033 


227 56 


40.63 


032 


293 11 


59.67 


056 


320 40 


21.94 


064 


000 00 


00.00 


063 


012 17 


26.82 


039 


028 45 


59.38 


034 


051 39 


17.13 


056 


101 43 


52.57 


057 


137 08 


38.24 


062 


295 02 


13.52 



Station 



From 



■ 'ion 



Station 



To 






To 






061 



062 



063 



033 


000 


00 00.00 


059 


007 


r ;i 38 52 


056 


038 


27 ',4 13 


0V,; 


062 


29 01 .54 


063 


071 


29 19 81 


034 


084 


19 4', Of, 


059 


092 


17 30 84 


0',0 


1 32 


20 56.72 


057 


146 


55 13 77 



063 



064 



000 000 00 00 00 



062 


041 


45 11.15 


004 


152 


N 


039 


244 


l 


099 


270 


24 07 44 


056 


J27 


14 52 77 


034 




• 


056 


054 


■ 


039 


035 


01 20.54 


063 


061 


00 17.00 


000 


076 


2', 20.03 


035 


356 


47 40.25 



Table 2B.—Preearlhquake measured length\ 



Station 



From 



To 



Measured 
length 



m 

1 3 * 12988.206 

1 17 * 29502 131 

16 56 1139 270 

31 32 1049 944 

31 34 19695.796 

34 64 23866.161 

39 63 5237.752 

60 63 13700.048 

* LAC adjusted length. 

vey. The corrections to the measured lengths are 
listed in tables 6A and 6B for preearthquake and 
postearthquake surveys, respectively. 

Adjusted geographic positions and plane coordi- 
nates, based on the California Plane Coordinate Sys- 
tem Zone 7. are listed in tables 7A (preearthquake) 
and 7B (postearthquake) . From these listings, the 
position shifts were computed for stations common 
to the preearthquake and postearthquake surveys. 
They are given in table 8A. Table 9A lists the error 
ellipses and 95-percent confidence levels as they refer 
to station Cahuenga 2, and figure 2A illustrates the 
position vectors and error ellipses between the 
preearthquake and postearthquake surveys. The posi- 
tion changes of greatest significance were in the areas 
of surface faulting, and the maximum change oc- 
curred at station Pacoima L-l. Because independent 
orientation was not available for each survey, some 
uncertainty was introduced into the direction of the 
position vectors most distant from the control. Fig- 
ure 2A indicates a possibility of weakness in the 
orientation of the net. 

Parameters of strain were computed using ad- 
justed data for triangles formed by common stations; 
these parameters are listed in table 10. An 



Horizontal Crustal Movements 



251 



explanation of the method of computing strain and 
its interpretation is given by Pope (1969) . Figures 
3A and 3B illustrate the maximum positive shear 
(y) gi yen m table 10. Maximum shear and are the 
components least affected by errors of orientation 
and scale. The orientation of maximum shear is 45° 
clockwise from the orientation of maximum exten- 
sion (0e,) • Because the position shifts are so large in 
the area of surface breakage, a more detailed break- 
down of the area should be used to clarify the shear 
adequately. Figure 3A shows the area where y 
amounts to more than one part in 20,000. 

Figure 3B illustrates y for all triangles in which 
shear is less than one part in 20,000. The outstand- 
ing feature of this illustration is the consistent pat- 
tern of shear in the Newhall-Saugus area. To sub- 
stantiate the fact that the adjustments do not 
significantly affect these results, computations for 
shear — using a variation of Frank's (1966) formulas 
for unadjusted observations — were made as an inde- 
pendent check. The pattern of y obtained from these 
computations is essentially the same. 

Figure 4 illustrates the principal axes of strain. 
The pattern for the Newhall-Saugus area is clear, 
but other areas are not uniform. 

Adjustment 2 

Adjustment 2 required that position shifts for the 
preearthquake survey be the same position shifts as 
in the postearthquake survey for the following sta- 
tions: Calabasas, Flint, Hauser, Loma Verde, Paci- 
fico, Pelona, Pelona ECC 2, Pico L-9A, Pico L-9 
AUX 2 ECC 1, Red, San Fernando, Sawmill, Warm 
Springs, Whitaker, and WPK A-7A AUX 1. To sat- 
isfy these conditions and to allow freedom of move- 
ment at all stations except Cahuenga 2, it was neces- 
sary to adjust the preearthquake and postearthquake 
surveys simultaneously. A variance-covariance matrix 
for this adjustment was not considered essential. 

Results 

The corrections applied to the horizontal direc- 
tions are given in table 5C for the preearthquake 
survey and in table 5D for the postearthquake sur- 
vey. The corrections applied to the measured lengths 
are listed in tables 6C and 6D for the preearthquake 
and postearthquake surveys, respectively. 



Tables 7C and 7D list the adjusted geographic po- 
sitions, and figure 2B illustrates the vectors for the 
position differences listed in table 8B. Vectors in the 
areas of surface faulting are very similar to the vec- 
tors in figure 2A for adjustment 1. However, the re- 
quirement that the position shift at stations on the 
west side of the net for the preearthquake survey be 
equal to the position shift at the respective stations 
in the postearthquake survey increases the residuals 
at some stations in both surveys. The increase is 
greater than expected from random error alone, par- 
ticularly at station San Fernando. Adjustment 3 is 
the response to this analysis. 

Adjustment 3 

In adjustment 3, the conditional equations affect- 
ing position changes at stations Chatsworth, San Fer- 
nando, Pico L-9A, and Pico L-9 AUX 2 ECC 1 
were removed. All other input data for the preearth- 
quake and postearthquake surveys remained the 
same as in adjustment 2. A variance-covariance ma- 
trix was also added to obtain error ellipses. 

Results 

The corrections applied to the horizontal direc- 
tions are given in table 5E for the preearthquake 
survey and in table 5F for the postearthquake sur- 
vey. The corrections applied to the measured lengths 
are listed in tables 6E and 6F for the preearthquake 
and postearthquake surveys, respectively. 

Tables 7E (preearthquake) and 7F (postearth- 
quake) list the adjusted geographic positions and 
plane coordinates. The position differences between 
the two surveys, as determined by adjustment 3, are 
given in table 8C. Table 9B lists the error ellipses 
and 95-percent confidence regions, and figure 2C il- 
lustrates the position vectors and error ellipses. Re- 
moving the conditional equations at the four stations 
permits the adjusted postearthquake positions to 
shift approximately 0.5 foot in a westward direction 
from the adjusted preearthquake positions. The pat- 
tern of vectors at stations in the Newhall-Saugus 
area is similar to the pattern of adjustment 1. 

CONCLUSIONS 

The pattern of movement of stations in the area 
of surface breakage should be interpreted with a 



252 San Fernando Earthquake of 1971 



.'.." " 


















'• 






















— I'll 








m 




- \ 




- _ 


" — — ^- f_«_ 








n_ '.-./V, \\ 








1 — , 




V~7m , ^^^\. l\"/ /W 
















\ ^\" vVAr'v 






7 ^tL"~ 










\ r\_\H^ 4, 
















\ ^\?$kx— - 
\ ><Tr\ 












•- 






V '^^f ^4 741 -- /\\ 






v» 








\ 742. -../ XT\ ^^ 




^^7lJ^« 731 






\ 7*0 >/;■;■■ X \\ 
































i X'TrH 7» 

/ \\\ / 

,./ 710% / 

703 ]\ -»•.' X 


rj/y^n.... 
















/^'"' 










718 / 


/ 


.^?20" 


- 










/ 
/ 


/ 

/ 
/ 


■ '.719 










70 
















" . — ^£ 

702 




71*7 


ffl-' 


J. 












f 



Figure IB. — Postearthquake triangulation net. 



more detailed breakdown of topography. Displace- 
ments in this area are left lateral, with a maximum 
of 7 feet at station Pacoima L-l. The movement at 
station Pacoima No. 2 seems to be different, and the 
fact that the station is located on a high steep hill 
may have some significance. 

The following information was obtained from the 
1971 recovery notes: 



Station Remarks 

Bum Few small cracks in hill. 

East Small cracks in ground near station. 

Long Numerous small cracks in ground near 

vicinity of station. 

Newhall RM 3 disturbed by large crack in earth — 

tremendous amount of local earth dis- 
placement in immediate vicinity of 
station. 

Pacoima E-2 ECC 1 . . Few small cracks noted on the sides of the 
station hill. 

Pacoima L-l Several cracks and much upheaval of earth 

in the immediate area of the station. 



Horizontal Crustal Movements 



253 



Table 3A.—Postearthqaake observed horizontal directions 



Table 3A.—Postearthquake observed horizontal directions— Continued 



Station 



Observed 
direction 



Station 



Observed 
direction 



Station 



From 



To 



From 



To 



701 



702 



703 



704 



705 



706 



709 



711 



712 



713 



715 



717 



703 
706 
702 

701 
703 
706 
715 
717 

736 
738 
706 
702 
701 

705 
706 
709 
738 

706 
709 
704 
738 

715 
717 
702 
701 
703 
738 
709 
704 
705 

711 
712 
704 
738 
705 
706 

710 
713 
712 
709 

735 
738 
709 
710 
711 
713 

735 
712 
711 
736 
737 

721 
717 
702 
706 
738 

702 
736 
706 
715 
721 
719 
718 



000 00 00.00 

043 28 26.99 
093 43 43.84 

000 00 00.00 

044 34 10.81 
098 50 38.81 
116 55 47.54 
171 04 58.02 

000 00 00.00 
036 49 24.51 
052 59 48.91 
115 45 16.35 
157 27 21.12 

000 00 00.00 
048 52 29.59 
073 00 40.58 
277 22 15.59 

000 00 00.00 
003 02 01.49 
051 42 15.32 
075 55 19.23 



000 00 
023 11 
074 31 
105 26 
137 30 
263 04 
155 27 
246 33 
325 58 



00.00 
34.76 
55.31 
00.33 
00.96 
22.49 
45.57 
20.07 
35.54 



000 00 00.00 
033 33 01.18 
126 30 18.20 
134 24 43.01 
184 49 23.84 
191 16 32.92 

000 00 00.00 
178 00 17.66 
223 01 34.11 
293 54 49.06 

000 00 00.00 
046 16 51.11 
099 18 16.18 
149 54 25.67 
174 51 57.23 
269 32 33.34 

000 00 00.00 
051 07 10.44 
091 25 16.38 

230 27 26.70 

231 59 06.54 

000 00 00.00 

063 48 39.93 
125 06 45.61 
212 29 40.56 
261 01 53.84 

000 00 00.00 
043 10 33.89 
056 25 19.80 

064 32 45.50 
121 35 18.31 
169 00 07.61 
118 21 49.94 



718 



719 



720 



721 



724 

726 
727 
729 

730 

731 
732 



733 



734 



721 


000 00 00.00 


719 


093 02 52.78 


717 


172 29 06.18 


717 


000 00 00.00 


718 


049 55 29.04 


721 


085 28 57.02 


720 


165 57 08.89 


719 


000 00 00.00 


721 


045 29 09.34 


724 


126 08 52.10 


732 


000 00 00.00 


731 


003 21 29.41 


727 


053 32 50.37 


724 


088 57 20.55 


720 


140 11 19.61 


719 


194 13 57.65 


717 


241 20 12.49 


715 


300 29 00.04 


738 


330 28 21.97 


729 


000 00 00.00 


720 


230 21 45.04 


721 


278 28 04.33 


727 


314 23 33.73 


726 


339 08 58.21 


729 


000 00 00.00 


724 


115 16 16.78 


727 


157 08 45.73 


732 


229 43 39.36 


724 


000 00 00.00 


721 


108 40 01.26 


732 


177 33 04.84 


726 


246 37 54.68 


730 


000 00 00.00 


732 


028 39 23.01 


734 


094 47 52.74 


724 


316 05 06.47 


726 


359 57 45.82 


732 


000 00 00.00 


734 


080 18 39.83 


729 


130 20 43.78 


733 


080 11 55.44 


732 


000 00 00.00 


734 


078 51 54.02 


752 


000 00 00.00 


734 


033 01 12.04 


729 


070 28 18.20 


730 


091 28 11.41 


726 


091 30 20.16 


731 


131 07 46.95 


738 


287 44 54.35 


727 


129 50 36.57 


721 


187 24 45.46 


733 


033 01 04.33 


729 


000 00 00.00 


730 


035 16 03.20 


732 


076 36 58.96 


738 


100 03 54.96 


729 


000 00 00.00 


730 


035 10 04.51 


731 


073 22 52.73 


732 


076 24 25.08 


738 


099 48 31.97 



Observed 
direction 



Station 



Observed 
direction 



From 



To 



From 



To 



734 



735 



736 



737 



738 



739 



741 



743 



744 





744 


752 


157 53 36.86 


765 


174 48 37.51 


755 


184 01 46.29 745 


768 


211 29 16.35 


712 


000 00 00.00 


713 


038 25 23.58 


736 


058 53 47.56 


737 


059 46 24.02 746 


740 


082 55 17.94 


739 


138 51 18.88 


741 


147 28 41.43 


738 


245 19 41.58 


703 


000 00 00.00 


738 


236 13 09.35 


717 


285 26 35.04 


735 


232 49 29.46 


713 


262 48 30.20 747 


710 


292 33 01.55 


735 


000 00 00.00 


738 


002 55 43.42 


713 


030 38 03.22 


740 


299 51 01.14 


752 


308 17 59.43 


739 


331 52 50.70 748 


766 


255 22 09.26 


765 


255 22 09.25 


764 


263 02 29.79 


752 


000 00 00.00 


733 


028 59 35.90 


732 


080 16 31.68 


705 


174 48 54.28 749 


706 


215 59 23.60 


710 


231 21 50.66 


709 


231 30 57.05 


704 


247 58 06.96 


712 


257 37 48.67 


737 


274 03 05.36 750 


735 


276 40 38.86 


741 


308 16 16.69 


721 


130 24 44.54 


715 


181 27 14.43 


703 


254 14 38.89 


736 


273 38 24.53 


766 


322 28 07.12 


764 


318 47 50.97 


734 


028 56 55.56 751 


735 


000 00 00.00 


737 


072 47 57.82 


740 


089 40 05.34 


742 


138 16 33.67 


741 


204 00 58.54 752 


738 


000 00 00.00 


735 


050 33 20.98 


739 


065 56 57.81 


740 


114 45 08.05 


742 


154 10 24.59 


744 


197 55 30.36 


743 


234 44 21.29 


741 


000 00 00.00 


742 


067 40 14.64 


744 


121 20 34.04 


746 


159 41 31.73 


745 


185 00 23.50 


746 


000 00 00.00 753 


745 


063 59 49.49 


743 


101 41 23.37 



741 


123 31 58.04 


742 


173 21 07.17 


743 


000 00 00.00 


744 


078 38 35.39 


746 


139 10 36.14 


748 


158 21 33.49 


747 


187 56 09.08 


748 


000 00 00.00 


747 


072 19 11.88 


745 


113 46 25.79 


743 


129 16 56.42 


744 


169 14 36.71 


766 


285 50 17.74 


752 


028 15 31.84 


764 


271 39 40.07 


757 


330 22 54.15 


752 


359 59 59.51 


745 


146 49 09.08 


746 


236 36 21.45 


766 


265 46 20.43 


748 


271 23 56.69 


749 


356 10 02.67 


750 


309 56 36.79 


747 


000 00 00.00 


745 


025 50 35.20 


746 


072 53 12.84 


764 


153 43 46.11 


757 


211 50 17.16 


750 


266 43 26.59 


749 


305 06 57.23 


747 


000 00 00.00 


748 


040 20 47.59 


750 


070 48 37.69 


756 


125 39 25.27 


751 


153 17 43.61 


748 


000 00 00.00 


757 


091 04 37.54 


756 


161 17 17.34 


754 


187 05 04.75 


752 


205 28 17.22 


747 


311 49 13.60 


749 


248 51 20.02 


751 


201 56 19.18 


749 


000 00 00.00 


750 


050 35 52.96 


756 


123 39 14.97 


755 


168 30 08.99 


754 


198 36 18.13 


738 


000 00 00.00 


737 


039 25 22.19 


747 


049 08 07.18 


746 


061 40 49.98 


756 


103 54 24.31 


766 


111 53 08.31 


767 


139 45 28.58 


734 


267 01 59.06 


732 


332 31 37.27 


750 


072 43 48.07 


764 


089 49 20.21 


754 


139 13 48.55 


755 


158 09 31.50 


753 


207 39 49.16 


765 


111 54 44.55 


752 


000 00 00.00 


754 


050 11 48.36 



254 San Fernando Earthquake of 1971 



Table 3 A.—Poslearlhquuke observed horizontal directions— Continued 



Station 


Observed 


Station 








directi 










From 


To 


on 


From 


To 


air"" 






753 




/ 


// 


760 




< 


< i 


tt 




755 


109 22 


06.02 




757 


044 


16 


W) 46 


754 








761 












756 


000 00 


00.00 




767 


000 


00 


00.00 




759 


044 02 


39.07 




762 


007 


59 


47.06 




755 


084 53 


25 . 58 




7 r ,7 


078 


23 


r ,\ .40 




753 


175 34 


34 39 




760 


196 


15 


16.35 




752 


236 56 


44.67 




764 


216 


27 


18 34 




750 


332 03 


32 . 79 


762 












751 


314 55 


11 .49 




759 


000 


(id 


in) 00 


755 










758 


024 


06 


19 23 




734 


000 00 


00.00 




757 


084 


•i '. 


34 . 58 




753 


023 51 


47.51 




761 


143 


54 


58.76 




752 


044 59 


23.63 




763 


318 


16 


26.70 




754 


054 00 


20 . 34 


763 












751. 


093 00 


02 . 78 




762 


000 


00 


00 00 




759 


119 33 


06.51 




71,7 


161 


05 


44.96 




764 


132 39 


47.49 




759 


273 


20 


K, 50 




767 


180 32 


56.71 




758 


308 


11', 


52.74 




751 


073 55 


58 . 54 


764 












768 


243 18 


49.34 




768 


000 


HO 


00.00 


756 










755 


028 


45 


57.93 




750 


000 00 


00.00 




761 


034 


43 


26.37 




757 


050 09 


50.97 




757 


049 


21 


01 .76 




758 


102 08 


27.84 




752 


052 


45 


20.76 




759 


150 18 


17.77 




748 


077 


11 


53.07 




755 


177 37 


24.13 




746 


088 


01 


00 . 1 1 




754 


233 44 


13.48 




738 


101 


43 


52.76 




752 


255 21 


33.50 




737 


137 


05 


56.29 




751 


293 42 


23.25 




765 


295 


02 


10.49 




749 


322 24 


48.76 




767 


012 


17 


24.71 


757 








765 












764 


000 00 


00.00 




767 


000 0i 




762 


077 43 


26.32 




734 


012 


50 


24.56 




758 


141 34 


49.58 




752 


020 


48 


10.25 




756 


172 17 


40.06 




738 


051 


22 


05.80 




750 


231 55 


09.39 




764 


060 


59 


35.12 




748 


265 57 


23.43 




737 


075 


23 


02.35 




746 


277 23 


11.81 


766 












761 


027 18 


53.16 




737 


000 


00 


00.00 




760 


357 12 


56.36 




752 


305 


23 


37.74 




767 


108 42 


19.84 




747 


328 


24 


55.99 


758 










746 


332 


46 


03.39 




-759 


000 00 


00.00 




738 


335 


58 


36.33 




756 


088 12 


38.90 


767 












757 


185 31 


12.82 




768 


000 


00 


00.00 




762 


241 02 


33.38 




752 


118 


07 


32.78 




763 


304 01 


30.62 




755 


092 


05 


11.36 


759 










757 


173 


29 


27.46 




754 


000 00 


00.00 




759 


132 


10 


46.39 




756 


052 31 


23.78 




760 


197 


43 


03.06 




758 


096 08 


54.98 




761 


193 


42 


09.68 




762 


133 05 


08.28 




763 


177 


09 


08.98 




755 


286 23 


31.89 




764 


207 


43 


28.39 




763 


184 42 


19.49 




765 


249 


28 


38.33 




767 


207 28 


57.90 


768 










760 










734 


000 


in) 


00.00 




767 


000 00 


00.00 




755 


035 


51 


21.12 




761 


012 14 


22.24 




764 


076 


26 


20.60 



In ilu- Newhall Saugus area, there is right-lateral 

movement of at least r > foot. Since the preearth- 
quake observations lot this area were made in 1%3, 
the time interval is less than H yeais; and the 
good reason to believe that most of the move 
o(( uned at the time of the earthqual 

Even though some weakness in azimuth control 
may be deduced from the illustration (Tig. 2A of 
the free-adjustment vectors and 95-percent erroi el- 
lipses, the lesults of the fiee adjustments gi\e the 
best representation of the observed data. The as- 
sumption of no movement at all stations around the 
perimeter of the net requires target corrections to 
some distances and directions than would normally 
be expected to result horn random error. These 
[argei corrections were introduced at stations along 
the western side of the net. Allowing stations San 
Fernando, Chatsworth, Pico L-9 AUX 2 ECC 1, and 
Pico 1. 9A freedom of movement as explained in ad- 
justment 3 improves the relation of the movement 
vectors in the San Fernando-Newhall area. 



REFERENCES 

Frank, F. C, "On the Deduction of Earth Strains From Survey 
Data," Bulletin of the Seismological Society of America, Vol. 
56, No. 1, Feb. 1966, pp. 35-42. 

Pope, Allen J., "Strain Analysis of Horizontal Crustal Move- 
ments in Alaska Based on Triangulation Surveys Before and 
After the Prince William Sound Earthquake of March 27, 
1961," The Prince William Sound, Alaska, Earthquake of 
1964 and Aftershocks, Vol. Ill: Research Studies and Inter- 
pretive Results, Geodesy and Photogrammetry, Coast 
and Geodetic Survey, Environmental Science Services Ad- 
ministration, U.S. Department of Commerce, Washington, 
D.C., 1969, pp. 99-111. 

Savage, James C, correspondence from U.S. Geological Survey, 
Menlo Park, Calif., to Dept. of County Engineer, Los 
Angeles, Calif., Mar. 12, 1971. 



Horizontal Crustal Movements 



255 



Table 3B.—Postearthquake Geodimeter-measured distances in meters 



From 



To 



Distance 



From 



To 



Distance 



From 



To 



Distance 



701 702 

701 703 

701 706 

702 703 

702 706 

702 715 

702 717 

703 736 

704 705 

704 706 

704 707 

704 709 

704 738 

705 706 

705 709 

705 738 

706 707 

706 709 

706 715 

706 738 

709 711 

709 712 

709 738 

710 711 

710 712 

710 736 

710 738 

711 712 

711 713 

712 713 

712 735 

712 738 

713 735 

713 737 

715 738 

717 718 

718 721 

719 720 

720 724 

721 727 



12312.320 
12988.248 
23689.237 
18468.538 
18433.678 

17784.643 

17277.090 

8834.865 

6707.119 

5354.937 

4063.040 
5918.553 
2874.647 
5139.684 
7537 . 743 

6949.956 
3149.940 
2420.603 
5728.547 
7572.380 

4867.378 
4749.053 
8619.200 
3779.620 
6111.645 

10848.427 

13421 .494 

2777.813 

4280.273 

3037.845 

3805.260 

10595.807 

4888.063 

3492.387 

10030.937 

9546 . 200 

7177.706 

13991.396 

17855.019 

13993.997 



721 732 

721 738 

724 730 

727 730 

727 732 

729 730 

729 732 

729 734 

730 732 

730 734 

731 732 

731 734 

732 734 

732 738 

732 752 

733 738 

734 738 

734 752 

734 755 

734 768 

735 737 

735 738 

735 739 

735 740 

735 741 

736 738 

737 738 

737 739 

737 740 

737 752 

737 766 

738 741 

738 752 

738 764 

739 740 

739 741 

739 742 

740 741 

740 742 

741 742 



15466.399 
19822.690 
19012.978 
8677.040 
13335.795 

9754.135 

20746.517 
12979.516 
13054.013 
16875.648 

1049.944 
19695.934 
19520.397 

9930.636 
21216.619 

24074.486 
24119.961 
11690.213 
15646.220 
23866.176 

7557.594 
8427 . 302 
3728.717 
6600.029 
5717.114 

15944.742 

15966.080 

7768.221 

2991.420 

25079.104 

29334.857 
10810.436 
20501.246 
27174.347 
5467.488 

2106.121 
4796.027 
6620.000 
4268.324 
4374.583 



741 743 

741 744 

742 743 

742 744 

743 744 

743 745 

743 746 

744 745 

744 746 

745 746 

745 747 

745 748 

746 747 

746 748 

746 752 

746 757 

746 764 

746 766 

747 748 

747 752 

747 766 

748 750 

748 757 

748 764 

750 754 

750 757 

752 754 

752 755 

754 755 

755 767 

756 757 

756 758 

757 758 

757 760 

757 761 

758 762 



2489.515 
5714.684 
4665.227 
3959 . 540 
4009.449 

2500.442 
6113.238 
3665.062 
3873.355 
3998 . 506 

2647.091 
4999.769 
3006.661 
1795.146 
11557.006 

5948.545 
9442.006 
19312.904 
2997 . 346 
9626.233 

21882.673 
2506.212 
4476.773 
9559.881 
7081 .447 

3662.679 
2435.725 
7283.864 
5042.169 
5237.757 

4488.173 
2311.136 
3564 . 582 
5123.042 
3074.378 

3672.189 



250 San Fernando Earthquake of 1971 

Table 4 A. —Lines used for azimuth control 



Table lit— Average and RM • (flfUM Inn, fir ,h,u,n for 
fiu i riiiln/uakf arut bO§ti mthifuake turveyt 



Station 



Azimuth 



From 



To 



Survey 



J i .re 



o / // 



Calabasas Chatsworth 1 »2 03 03 88 Preearthquake 

Cahuenga 2 Flint 256 02 35.92 Pottearthquake . 



<) 99 
1.17 



Table 4C.—ElevatiotU oj stations used in reduction Of (.eodirruter distn, 



5 12 



Station no. 



Station name 



Elevation Station no. 



Station name 



ition 



701 Calabasas 

702 RESK-9A 

703 Chatsworth 

704 SyimarF-8 

705 Pacoima L- 1 . . . . 

706 PAC E-2 ECC 1 

707 SylmarI-12 

709 Reservoir 

710 Corner 2 

711 Bluff 

712 Mission Pt 

713 Ridge 2 

715 Pacoima 2 

717 Cahuenga 2 

718 Verdugo AUX . . 

719 Flint 

720 MTW E-10A. .. 

721 Sister Elsie 

724 Pacifico 

726 Parker AUX 2.. 

727 Mt. Gleason 

729 Hauser 

730 Parker 

731 Magic 

732 Port 

733 Pelona ECC 2... 

734 Pelona 

735 East 

736 Pico L-9A 



737 Pico L-9 AUX 2 ECC 1 



m 
496 6 

590 . 2 

704 . 2 

7 J6 9 

485 

413.9 

381 

394 . 7 

300.0 

502 . 5 

843.8 

1008.9 

393.3 

554.2 

932.5 

575.9 

1722.7 

1547.0 

2174.5 

1258.9 

1931.4 

1580.2 

1259.1 

1470.8 

1480.5 

1474.7 

1478.5 

678.4 

1137.0 

1136.7 



738 May 

7 J9 Edison 

740 Towsley . 

741 Newhall 

742 Lock... 

74 5 Saugus. . 

744 Yucca . . 

745 

746 

747 

748 

750 

752 



Foot 2 

Long 

Dry 

Bum 

Steer 

Deer 

753 House 

754 Brushy 

755 Red 

756 Powerhouse 

757 Charlie 

758 Taylor 

759 Elizabeth 

760 Cast C 

761 Fork 

762 Daires 

763 Necktie 

764 Loma Verde 

765 Whitaker 

766 WPK A-7A AUX 1 

767 Warm Springs 

768 Sawmill 



m 

874.0 
409. 
507.2 

451.2 

471.0 
570.7 
589.0 

1097.8 
858.2 

827. 
1217. 
679. 
641. 
665. 
804. 
524. 
526.7 
589.2 



1088 
760 
1255 
1254. 
1224. 
1680. 



1 Most elevations were determined by vertical angle observations; some are subject to slight revision after precise level data are made 
available. 



Horizontal Crustal Movements 



257 



Table 5 A.— Adjustment 1 corrections to preearthquake observed horizontal directions 





Station 


— v" 




Station 


.." 




Station 






Station 




Frorr 


To 




From 


To 


V 


From 


To 


— v" 


From 


To 


— v" 


1 






13 






21 






33 








2 


-0.67 




11 


0.52 




23 


0.50 




56 


0.51 




3 


0.14 




12 


-0.54 




31 


-0.01 




59 


0.14 




14 


0.47 




54 


-0.20 




56 


0.59 


34 








57 


0.06 




57 


0.22 


22 








26 


-0.29 


2 






14 








21 


0.37 




30 


0.24 




1 


0.63 




1 


-0.54 




23 


0.59 




31 


-1.01 




3 


0.43 




2 


0.22 




31 


-0.96 




35 


0.72 




14 


0.87 




3 


-0.65 


23 








36 


0.32 




15 


-0.24 




5 


0.17 




20 


-0.30 




39 


0.05 




16 


-0.23 




6 


0.37 




21 


-0.24 




56 


0.55 




17 


-0.75 




15 


0.00 




22 


-0.80 




60 


-1.05 




18 


-0.08 




16 


0.83 




24 


0.90 




64 


0.48 




57 


-0.63 




17 


-0.48 




26 


0.55 


35 






3 








57 


0.08 




30 


-0.09 




34 


-0.89 




1 


0.36 


15 








31 


-0.01 




36 


-0.36 




2 


-0.05 




2 


0.04 


24 








37 


0.16 




14 


0.65 




4 


0.00 




20 


-0.43 




38 


1.08 




16 


-0.75 




5 


-0.11 




23 


-0.72 




39 


0.22 




57 


-0.21 




6 


-0.13 




26 


1.15 




64 


-0.20 


4 








9 


0.89 


25 






36 








5 


-0.09 




14 


-0.44 




27 


-0.58 




34 


0.08 




6 


-0.01 




16 


-0.92 




28 


0.21 




35 


-0.01 




7 


0.30 




17 


0.43 




29 


0.38 




37 


0.49 




8 


-0.10 




18 


0.10 


26 








38 


— 0.56 




15 


-0.08 




21 


0.73 




23 


-0.68 


37 






5 








56 


-0.25 




24 


-0.76 




35 


-0.61 




4 


0.24 




57 


-0.34 




30 


0.36 




36 


0.17 




6 


0.05 


16 








34 


1.08 




38 


0.13 




7 


-0.20 




2 


-0.18 


27 








39 


0.41 




8 


0.01 




3 


-0.06 




25 


0.30 




40 


-0.08 




14 


-0.23 




6 


0.08 




28 


0.23 


38 








15 


0.14 




9 


0.99 




29 


-0.46 




35 


0.16 


6 








14 


-0.10 




30 


0.58 




36 


0.29 




4 


0.37 




15 


-0.74 




32 


-0.32 




37 


— 0.42 




5 


0.10 




17 


0.01 




33 


-0.32 




39 


-0.04 




7 


-0.33 




18 


-0.50 


28 








40 


0.02 




8 


-0.27 




21 


0.43 




27 


0.08 


39 








9 


0.29 




56 


0.09 




29 


-0.23 




34 


-0.79 




14 


0.03 




57 


-0.02 




30 


0.15 




35 


— 0.02 




15 


0.17 


17 






29 








37 


-0.05 




16 


-0.14 




2 


1.04 




25 


-0.85 




38 


0.07 




56 


-0.22 




14 


0.35 




27 


-1.06 




40 


0.87 


7 








15 


0.21 




28 


0.35 




41 


0.57 




4 


-0.84 




16 


-0.34 




30 


0.68 




42 


— 0.38 




5 


0.04 




18 


-0.38 




32 


0.16 




56 


0.25 




6 


0.40 




19 


-0.08 




33 


0.71 




60 


-0.77 




8 


0.40 




20 


-0.29 


30 








63 


0.63 


8 








21 


-0.51 




23 


0.09 




64 


-0.40 




4 


0.32 


18 








26 


-0.57 


40 








5 


0.09 




2 


-0.74 




27 


0.14 




37 


— 0.30 




6 


-0.23 




15 


-0.11 




28 


-0.43 




38 


0.11 


9 


7 


-0.16 




16 


-0.07 




29 


0.26 




39 


-0.25 








17 


0.70 




31 


-0.36 




41 


0. 14 




6 


-0.27 




19 


-0.39 




32 


0.44 




42 


0.29 




10 


-0.45 




20 


0.75 




33 


0.28 


41 








11 


0.45 




21 


-0.03 




34 


0.15 




39 


— 0.38 




12 
15 

16 


0.23 
0.53 
0.31 


19 


56 
17 


-0.12 
0.76 


31 


21 


-0.22 




40 
42 
43 


-0.54 

0.35 

— 0. 11 


10 


56 


-0.79 




18 


-0.20 




22 


0.69 




44 


0.66 








20 


-0.45 




23 


0.40 


42 








9 


0.04 




21 


-0.10 




30 


0.33 




39 


— 0.15 




11 


-0.71 


20 








32 


-1.65 




40 


0.21 


11 


12 


0.68 




17 


-0.02 




34 


-1.08 




41 


-0.04 








18 


-0.16 




56 


1.52 




43 


— 0.17 




9 


0.18 




19 


0.67 


32 








44 


0. 15 




10 


-0.05 




21 


-0.75 




27 


0.02 


43 








12 


-0.45 




23 


0.17 




29 


-0.30 




41 


— 0. 13 




13 


0.91 




24 


0.73 




30 


-0.50 




42 


0.00 




56 


0.79 




57 


-0.65 




31 


1.50 




44 


0.02 


12 


57 


-1 .36 


21 








33 


0.22 




45 


-0.22 








15 


-0.23 




56 


-1.18 




46 


0.33 




9 


0.23 




16 


-0.89 




59 


0.21 


44 








10 


0.86 




17 


-0.43 


33 








41 


— 0.79 




11 


-0.61 




18 


-0.05 




27 


-0.10 




42 


0.29 




13 


0.85 




19 


0.65 




29 


-0.79 




43 


— 0.31 




54 


-0.19 




20 


0.52 




30 


-0.58 




45 


0.68 




56 


— 1.14 




22 


-0.65 




32 


0.82 




46 


0.14 



258 



San Fernando Earthquake of 1971 







Table 5/1. 


—A djuslment 


/ corrections to pre earthquake observed horizrmtrit ditrition t ontinued 








Station 




Station 




Station 




Sta' 












„» 












.,* 


From 


To 


V 


From 


V 

To 


From 


Jo 


V 


1 rom 


To 


V 


45 






51 




56 






59 








43 


-0.27 




52 -0.11 




18 


0.40 




32 






44 


-0.38 




53 -0.11 




21 


22 




33 


-0.24 




46 


0.11 




55 31 




31 


19 




56 


-0 69 




47 


-0.15 


52 






32 


-0.54 




58 


-0 




48 


0.72 




49 0.60 




33 


-0 05 




61 


81 


46 








50 0.23 




34 


-0.08 




63 


08 




43 


. 1 5 




51 30 




39 


-0.73 


60 








44 


0.31 




53 -0.07 




52 


1 .06 




34 


-0 70 




45 


-0.33 




54 -0.06 




54 


08 




39 


03 




47 


-0.25 




55 . 36 




57 


0.18 




56 


28 




48 


0.12 




56 -0.74 




58 


-1.67 




57 


-0 06 


47 








57 -0.61 




59 


- 34 




62 


-0 




45 


-0.22 


53 






60 


-1 17 




63 


0.35 




46 


0.46 




51 -0.26 




61 


0.84 




64 


55 




48 


-0.13 




52 -0.48 




64 


-0.60 


61 








49 


-0.65 




54 0.83 


57 








33 


-0.78 




50 


0.53 




55 0.26 




1 


-1.09 




56 




48 








57 -0.38 




2 


-0.88 




58 


0.13 




45 


-0.18 


54 






3 


93 




59 


0.06 




46 


0.31 




12 -0.07 




11 


-0.30 


62 








47 


-0.14 




13 1.53 




13 


1 .59 




34 


-0 76 




49 


-0.25 




52 -0.01 




14 


-0.42 




57 


1.10 




50 


0.27 




53 -0.77 




15 


- 1 . 06 




59 


11 


49 








55 -0.40 




16 


-0.66 




60 


-0.75 




47 


-0.01 




56 0.56 




20 


-0.03 




63 


0.31 




48 


0.40 




57 -0.85 




52 


0.81 


63 








50 


-0.28 


55 






53 


-0.03 




39 


-0.02 




51 


-0.20 




51 -0.80 




54 


0.00 




58 


-0.52 




52 


-0.62 




52 0.05 




55 


0.79 




59 


-0.69 




56 


0.74 




53 -0.11 




56 


— 0.04 




60 


0.66 


50 








54 0.65 




59 


0.50 




62 


-0.02 




47 


-0.41 




57 0.23 




60 


-0.89 




64 


0.59 




48 


0.22 


56 






62 


0.79 


64 








49 


0.08 




6 0.82 


58 








34 


0.66 




51 


-0.05 




9 -0.61 








35 


-0.55 




52 


0.19 




11 0.20 




56 


— 0.01 




39 


-0.03 


51 








12 -0.06 




59 


-0.16 




56 


0.03 




49 


-0.41 




15 1.58 




61 


-0.14 




60 


-0.22 




50 


0.34 




16 -0.20 




63 


0.31 




63 


0.11 



Horizontal Crustal Movements 



259 



Table 5B.— Adjustment 1 corrections to postearthquake observed horizontal directions 





Station 






Station 


\," 




Station 






Station 


v" 


From 


To 


V 


From 


To 


V 


From 


To 


V 


From 


To 




701 






719 






735 






746 








702 


0.07 




717 


-0.45 




737 


-0.19 




747 


-0.05 




703 


0.44 




718 


-0.17 




738 


-0.40 




748 


0.26 




706 


-0.51 




720 


0.28 




739 


-0.21 




752 


0.61 


702 








721 


0.35 




740 


-0.32 




757 


0.14 




701 


0.24 


720 








741 


0.08 




764 


0.56 




703 


0.26 




719 


-0.51 


736 








766 


-1.21 




706 


-0.67 




721 


0.41 




703 


-0.90 


747 








715 


-0.54 




724 


0.11 




710 


1.15 




745 


-1.01 




717 


0.71 


721 








713 


1.20 




746 


-0.59 


703 








715 


-1.62 




717 


-0.94 




748 


0.00 




701 


0.84 




717 


-0.41 




735 


0.49 




749 


1.82 




702 


-0.49 




719 


0.17 




738 


-1.02 




750 


0.06 




706 


-0.21 




720 


-0.16 


737 








752 


-0.66 




736 


0.26 




724 


0.48 




713 


0.60 




766 


0.41 




738 


-0.39 




727 


-0.46 




735 


-0.16 


748 






704 








731 


0.82 




738 


-0.47 




745 


-0.12 




705 


0.03 




732 


0.97 




739 


0.67 




746 


-0.08 




706 


0.03 




738 


0.21 




740 


-0.66 




747 


0.15 




709 


-0.05 


724 








752 


-0.29 




749 


-0.47 




738 


0.01 




720 


-0.11 




764 


0.34 




750 


0.07 


705 








721 


0.48 




765 


-0.02 




757 


0.23 




704 


0.34 




726 


-0.68 




766 


-0.03 




764 


0.23 




706 


0.05 




727 


-0.15 


738 






749 








709 


0.25 




729 


0.46 




703 


0.58 




747 


-0.75 




738 


-0.61 


726 








704 


-0.02 




748 


0.49 


706 








724 


-0.16 




705 


-0.01 




750 


-0.04 




701 


0.99 




727 


0.35 




706 


-0.62 




751 


0.60 




702 


0.78 




729 


-0.02 




709 


-0.45 




756 


-0.29 




703 


1.60 




732 


-0.16 




710 


-0.51 


750 








704 


-0.38 


727 








712 


1.27 




747 


-0.03 




705 


-0.98 




721 


0.44 




715 


0.40 




748 


-0.06 




709 


-0.88 




724 


1.11 




721 


-0.39 




749 


-0.43 




715 


-0.63 




726 


-0.42 




732 


0.27 




751 


-0.38 




717 


0.24 




732 


-1.12 




733 


-0.47 




752 


0.42 




738 


-0.74 


729 








734 


-1.79 




754 


0.29 


709 








724 


-1.30 




735 


0.68 




756 


0.11 




704 


0.51 




726 


0.21 




736 


0.60 




757 


0.08 




705 


0.55 




730 


0.21 




737 


-0.08 


751 








706 


-0.08 




732 


1.26 




741 


1.16 




749 


0.02 




711 


-1.46 




734 


-0.38 




752 


-0.05 




750 


-0.27 




712 


0.01 


730 








764 


-0.72 




754 


-0.29 




738 


0.45 




729 


-0.17 




766 


0.18 




755 


0.42 


711 








732 


-0.10 


739 








756 


0.11 




709 


0.45 




733 


0.14 




735 


0.18 


752 








710 


0.48 




734 


0.13 




737 


-0.89 




732 


-0.58 




712 


-0.03 


731 








740 


-0.11 




734 


-0.38 




713 


-0.89 




732 


0.26 




741 


0.23 




737 


0.33 


712 








734 


-0.25 




742 


0.59 




738 


0.17 




709 


-0.18 


732 






741 








746 


-0.24 




710 


-0.92 




721 


0.69 




735 


0.49 




747 


-0.13 




711 


0.73 




726 


-0.11 




738 


-0.66 




750 


1.13 




713 


-0.14 




727 


0.10 




739 


-0.58 




753 


0.50 




735 


0.12 




729 


0.62 




740 


-0.38 




754 


-0.11 




738 


0.40 




730 


-0.11 




742 


0.58 




755 


1.20 


713 








731 


-0.23 




743 


0.40 




756 


-1.20 




711 


1.41 




733 


-1.44 




744 


0.14 




764 


-1.09 




712 


-0.12 




734 


-1.26 


743 








765 


-0.77 




735 


0.44 




738 


1.19 




741 


-0.80 




766 


2.04 




736 


0.08 




752 


0.57 




742 


-0.14 




767 


-0.88 




737 


-1.82 


733 








744 


-0.39 


753 






715 








729 


-1.09 




745 


0.41 




752 


-0.27 




702 


-0.34 




730 


-0.31 




746 


0.94 




754 


-0.23 




706 


-0.60 




732 


0.39 


744 








755 


0.49 




717 


0.24 




738 


1.00 




741 


-0.69 


754 








721 


0.25 


734 








742 


0.32 




750 


0.14 




738 


0.45 




729 


0.15 




743 


-0.39 




751 


0.32 


717 








730 


0.16 




745 


0.32 




752 


0.06 




702 


0.71 




731 


1.32 




746 


0.44 




753 


-0.06 




706 


0.02 




732 


-0.43 


745 








755 


0.22 




715 


-0.99 




738 


-0.26 




743 


-0.85 




756 


-0.52 




718 


0.33 




752 


0.14 




744 


0.36 




759 


-0.17 




719 


-0.49 




755 


0.51 




746 


0.11 


755 








721 


0.51 




765 


-0.93 




747 


0.63 




734 


-0.65 




736 


-0.07 




768 


-0.66 




748 


-0.24 




751 


-0.31 


718 






735 






746 








752 


0.15 




717 


0.16 




712 


0.27 




743 


0.85 




753 


-0.03 




719 


-0.49 




713 


-0.09 




744 


-0.96 




754 


0.27 




721 


0.33 




736 


0.86 




745 


-0.20 




756 


-0.18 



200 



San Fernando Earthquake of 1971 



Table fit.— Adjustment 1 corrections to postearthquake observed horizontal directions— Continued 





Station 


,," 




Station 


■u" 




Station 






Station 




From 


To 




From 


To 




From 


To 




1 .",;/. 


To 




755 






7 r ;!i 






v,-i 






765 








759 


0.17 




750 


0.10 




758 


0.41 




7 r j2 


41 




764 


-0.08 




757 


-1.00 




759 


-0.14 




764 


00 




767 


0.60 




759 


0.05 




761 


10 




767 


-0 




768 


0.08 




762 


-0.07 




763 


-0.15 


766 






756 








763 


0.87 


763 








737 


1.36 




749 


0.57 


759 








758 


-0.72 




738 


-0.35 




750 


-0.11 




754 


-0.72 




759 


-0.66 




746 


-1.74 




751 


0.34 




755 


0.32 




762 


0.77 




747 


% 




752 


0.43 




756 


0.03 




767 


60 




752 


-0.12 




754 


0.52 




758 


-0.03 


764 






767 








755 


-1.87 




762 


0.17 




737 


0.14 




752 


0.31 




757 


-0.25 




763 


0.75 




738 


08 




755 


0.19 




758 


0.22 




767 


-0.53 




746 


0.10 




757 


-0.63 




759 


0.16 


760 








748 


0.31 




759 


-0.26 


757 








757 


-0.13 




752 


0.40 




760 


— 0.13 




746 


-0.15 




761 


0.08 




755 


0.13 




761 


-1.14 




748 


-1.18 




767 


0.06 




757 


0.29 




703 


-0.24 




750 


-0.21 


761 








761 


-2.02 




764 


87 




756 


-0.26 




757 


-0.92 




765 


-0.04 




765 


0.16 




758 


0.30 




760 


-0.01 




767 


0.80 




768 


0.84 




760 


0.07 




762 


0.39 




768 


-0.78 


768 








761 


0.42 




764 


0.85 


765 








734 


-0.30 




762 


-0.27 




767 


-0.29 




734 


0.27 




755 


0.20 




764 


-0.03 


762 








737 


-1.37 




764 


0.36 




767 


1.32 




757 


-0.23 




738 


0.43 




767 


-0.27 



Table 6 A.— Adjustment 1 corrections to preearthquake observed lengths (v's) in meters 





Station 




Observed 


Weight 


v in 


v in 


Adjusted 










length 


factor 


seconds 


meters 


length 


1 part in 








From 




To 














1 




3 


12988.206 


1.0 


-0.18 


-0.011 


12988.195 


1150,000 


1 




17 


29502.131 


1.0 


0.21 


0.030 


29502.161 


973,000 


16 




56 


1139.270 


0.3 


1.49 


0.008 


1139.278 


139,000 


31 




32 


1049.944 


0.1 


-13.91 


-0.071 


1049.873 


15,000 


31 




34 


19695.796 


2.4 


-0.11 


-0.011 


19695.785 


1815,000 


34 




64 


23866.161 


2.4 


0.18 


0.021 


23866.182 


1152,000 


39 




63 


5237.752 


0.6 


-0.44 


-0.011 


5237.741 


469,000 


60 




63 


13700.048 


1.6 


-0.11 


-0.007 


13700.041 


1954,000 



Number of lengths = 8 

Maximum length = 29502 .131 
Minimum length = 1049.944 
Average length =13397.413 



STATISTICS 
Maximum positive v in seconds = 1 .49 
Maximum negative v in seconds = — 13.91 
Average length v in seconds = 2 . 08 

Maximum positive v in meters = 0.030 



Maximum negative v in meters = —0.071 
Average length v in meters = 0.021 

The sum of pw in seconds = 2 . 5678 

The sum of vv in seconds = 1 96 . 0064 



Horizontal Crustal Movements 



261 





Table 6 It. 


-Adjustment 1 


corrections to 


postearthquake 


observed lengths 


(v's) in meters 






Station 


Observed 


Weight 


v in 


v in 


Adjusted 








length 


factor 


seconds 


meters 


length 


1 part in 






From 


To 














701 


702 


12312.320 


1.0 


-0.35 


-0.021 


12312.299 


592,000 


701 


703 


12988.248 


1.0 


0.34 


0.022 


12988.270 


604 


,000 


701 


706 


23689.237 


1.0 


0.38 


0.043 


23689.280 


547 


,000 


702 


703 


18468.538 


1.0 


0.09 


0.008 


18468.546 


2196 


,000 


702 


706 


18433.678 


1.0 


0.61 


0.054 


18433.732 


338 


,000 


702 


715 


17784.643 


1.0 


0.12 


0.010 


17784.653 


1765 


,000 


702 


717 


17277.090 


1.0 


0.02 


0.002 


17277.092 


8800 


,000 


703 


736 


8834.865 


1.0 


0.77 


0.033 


8834.898 


266 


,000 


704 


705 


6707.119 


1.2 


0.35 


0.011 


6707.130 


592 


,000 


704 


706 


5354.937 


0.8 


-0.10 


-0.003 


5354.934 


2013 


,000 


704 


707 


4063.040 


0.6 


0.01 


0.000 


4063.040 


22108 


,000 


704 


709 


5918.553 


0.8 


-0.48 


-0.014 


5918.539 


433 


,000 


704 


738 


2874.647 


0.4 


-0.49 


-0.007 


2874.640 


423 


,000 


705 


706 


5139.684 


0.8 


-0.22 


-0.006 


5139.678 


918 


,000 


705 


709 


7537.743 


1.2 


-0.34 


-0.012 


7537.731 


611 


,000 


705 


738 


6949.956 


0.7 


0.21 


0.007 


6949 . 963 


989 


,000 


706 


707 


3149.940 


0.8 


-0.02 


-0.000 


3149.940 


12227 


,000 


706 


709 


2420.603 


0.7 


-1.22 


-0.014 


2420.589 


169 


,000 


706 


715 


5728.547 


1.0 


0.25 


0.007 


5728.554 


825 


,000 


706 


738 


7572.380 


0.7 


-0.72 


-0.027 


7572.353 


286 


,000 


709 


711 


4867.378 


0.9 


-1.17 


-0.028 


4867.350 


176 


,000 


709 


712 


4749.053 


0.6 


-0.37 


-0.009 


4749.044 


551 


,000 


709 


738 


8619.200 


0.7 


0.09 


0.004 


8619.204 


2270 


,000 


710 


711 


3779.620 
6111.645 
10848.427 
13421.494 
2777.813 
4280.273 
3037.845 


0.7 
0.7 
0.8 
1.0 
0.5 
0.5 
0.6 


-0.05 
-0.16 
-0.99 
-1.19 
-1.29 
-0.46 
0.40 


-0.001 
-0.005 
-0.052 
-0.078 
-0.017 
-0.010 
0.006 


3779.619 
6111.640 
10848.375 
13421.416 
2777.796 
4280.263 
3037.851 


3984 
1269 
209 
173 
160 
449 
510 


,000 


710 


712 


,000 


710 


736 


,000 


710 


738 


,000 


711 


712 


,000 


711 


713 


000 


7!2 


713 


000 


712 


735 


3805.260 

10595.807 

4888.063 

3492 . 387 

10030.937 

9546.200 

7177.706 

13991 .396 

17855.019 


0.7 
1.1 
0.7 
0.7 
1.0 
1.1 
0.8 
0.9 
1 .4 


0.06 

-0.22 

-0.07 

-0.10 

0.69 

0.02 

-0.67 

0.26 

0.08 


0.001 

-0.011 

-0.002 

-0.002 

0.033 

0.001 

-0.023 

0.018 

0.007 


3805.261 

10595.796 

4888.061 

3492 . 385 

10030.970 

9546.201 

7177.683 

13991.414 

17855.026 


3220 
938 

3134 

2094 

300 

10091 

308 

798 

2561 


,000 


712 


738 


000 


713 


735 


000 


713 


737 


000 


715 


738 


000 


717 


718 


000 


718 


721 


000 


719 


720 


000 


720 


724 


000 


721 


727 


13993.997 


1.3 


-0.68 


-0.046 


13993.951 


306 


000 


721 


732 


15466.399 


1.6 


0.35 


0.026 


15466.425 


598 


000 


721 


738 


19822.690 


1.5 


0.43 


0.041 


19822.731 


481 


000 


724 


730 


19012.978 


1.2 


-0.99 


-0.092 


19012.886 


207 


000 


727 


730 


8677.040 


0.8 


1.09 


0.046 


8677.086 


189 


000 


727 


732 


13335.795 


1.0 


-0.12 


-0.008 


13335.787 


1705 


000 


729 


730 


9754.135 


1.1 


-0.03 


-0.001 


9754.134 


7422 


000 


729 


732 


20746.517 


1.8 


-0.27 


-0.027 


20746.490 


755 


000 


729 


734 


12979.516 


1.5 


-0.38 


-0.024 


12979.492 


541 


000 


730 


732 


13054.013 


1.4 


0.06 


0.004 


13054.017 


3180 


000 


730 


734 


16875.648 


1.5 


0.35 


0.028 


16875.676 


596 


000 


731 


732 


1049.944 


0.4 


0.05 


0.000 


1049.944 


4303 


000 


731 


734 


19695.934 


1.8 


0.05 


0.004 


19695.938 


4499 


000 


732 


734 


19520.397 


1.8 


-0.27 


-0.025 


19520.372 


775 


000 


732 


738 


9930.636 


1.2 


-1.23 


-0.059 


9930.577 


167 


000 


732 


752 


21216.619 


1.5 


-0.73 


-0.075 


21216.544 


284 


000 


733 


738 


24074.486 


1.7 


0.29 


0.034 


24074.520 


709 


000 


734 


738 


24119.961 


1.7 


0.23 


0.027 


24119.988 


906 


000 


734 


752 


11690.213 


1.2 


-0.13 


-0.007 


11690.206 


1625 


000 


734 


755 


15646.220 


1.5 


0.42 


0.032 


15646.252 


496 


000 


734 


768 


23866.176 


1.8 


0.31 


0.036 


23866.212 


660 


000 


735 


737 


7557.594 


0.9 


-0.28 


-0.010 


7557.584 


728 


000 


735 


738 


8427 . 302 


0.9 


-0.53 


-0.022 


8427.280 


386 


000 


735 


739 


3728.717 


0.6 


-1.20 


-0.022 


3728.695 


172 


000 


735 


740 


6600.029 


1.0 


-0.37 


-0.012 


6600.017 


562 


000 


735 


741 


5717.114 


0.9 


-0.32 


-0.009 


5717.105 


636 


000 


736 


738 


15944.742 


1.7 


0.55 


0.043 


15944.785 


373 


000 


737 


738 


15966.080 


1.7 


0.81 


0.063 


15966.143 


254 


000 


737 


739 


7768.221 


0.8 


0.17 


0.006 


7768.227 


1241 


000 


737 


740 


2991.420 


0.6 


-0.19 


-0.003 


2991 .417 


1078 


000 


737 


752 


25079.104 


1.9 


0.77 


0.093 


25079.197 


269 


000 


737 


766 


29334.857 


1.0 


0.24 


0.034 


29334.891 


861 


000 


738 


741 


10810.436 


0.9 


-0.52 


-0.027 


10810.409 


394 


000 


738 


752 


20501.246 


1.8 


0.30 


0.030 


20501.276 


686 


000 


738 




27174.347 


1.6 


0.47 


0.062 


27174.409 


436 


000 


739 


740 


5467.488 
2106.121 


0.7 
0.6 


-0.51 
-0.91 


-0.014 
-0.009 


5467.474 
2106.112 


401, 
226, 


000 


739 




000 



262 



San Fernando Earthquake of 1071 



Table 6B.— Adjustment I correction* to pottearthqualu obierved i< ngthi (i/§) in mettn—4. minimi it 



Station 


( >\i- • 


Weight 


v in 


v in 










[( ngth 


fat toi 


,nds 


in<-tcr» 


kagdi 


1 part in 






From 


To 














739 


742 


4796.027 


1.0 


-0.4-, 


-0 Oil 


47'**, 016 




740 


741 


6620.000 


8 


-1.13 


-0 036 


6619 964 


000 


740 


742 


4268 124 


0.6 


16 


ooj 


42*,;; 


1301 ,000 


741 


742 


4 571 583 


9 


23 


005 


4 574 


000 


741 


74:5 


2489 51 5 


o 1 


-d 


-0.006 


2489 


KM) 


741 


744 


5714 684 


1 ,2 


-0 61 


-0.017 


0714 667 


'XX) 


742 


743 


4665.227 


9 


0.17 


00 1 


231 


1231,000 


742 


744 


3959 540 


i) c, 


1 08 


0.021 


J959 


191,000 


74:i 


744 


400') Wi 
2500.442 


1 .0 
0.6 


0.47 
-0 58 


i) 009 
-0 <XJ7 


4009 458 
2500 435 


44 5 >**) 


743 


745 


M) 


74:5 


746 


6113.238 


11 


0.06 


002 


6113 240 


'//J 


744 


745 


3665.062 


0.8 


0.18 


0.003 




11)8,000 


744 


746 


387 I 


0.8 


-0.01 


-0 000 


3873 155 


16216,000 


745 


746 


3998. 506 


0.9 


-0 70 


-0 014 


492 


000 


745 


747 


2647 U'M 


7 


-0.47 


-ii 006 


2647 085 


441,000 


745 


748 


4999 769 


0.9 


-0.32 


-0.008 


4999 70 1 


000 


746 


747 


3006.661 


0.8 


0.90 


'il 5 


1006 '.74 


228,000 


746 


748 


1795. 146 


0.5 


-0.74 


-0.006 


1795 140 


280,000 


746 


752 


11557 006 


1 .0 


0.09 


005 


11557 Oil 


2 146 . 000 


746 


757 


5948 545 


1 ,0 


0.42 


012 


557 


489. 000 


746 


764 


9442.006 


11 


0.07 


0.003 


9442.009 


}'>4 1 , 000 


746 


766 


19312.904 


1 


-0.15 


-0 014 


19312.890 


1378,000 


747 


748 


2997 


0.7 


1.41 


020 


166 


147,000 


747 


752 


9626.233 


0.9 


0.14 


006 


2 59 


1500,000 


747 


766 


21882.673 


1.0 


-0.06 


-0 006 


21882.667 


3554, 000 


748 


750 


2506.212 


0.7 


0.12 


ool 


21 5 


1725,000 


748 


757 


4476.77:5 


0.9 


-0.23 


-0.005 


4476.768 


878,000 


748 


764 


9559.881 


1.2 


0.00 


000 


• 881 


8488 5 , 000 


750 


754 


7081 .447 


1.0 


-0.33 


-0.011 


7081 4 56 


ooo 


750 


757 


3662.679 


0.8 


0.05 


0.001 


1662 680 


3977, 000 


752 


754 


2435.725 


5 


0.16 


1 


24 55.727 


1304,000 


752 


755 


728:5.864 


1.2 


0.07 


0.002 


7283.866 


2940,000 


754 


755 


5042. 169 


0.7 


-0.58 


-0.014 


5042 . 1 55 


358,000 


755 


767 


5237 . 757 


1.2 


0.09 


0.002 


5237.759 


2350,000 


756 


757 


4488 . 1 73 


1.0 


-0.24 


-0.005 


4488.168 


843,000 


756 


758 


2311 .136 


0.6 


-1 .82 


-0.020 


2311.116 


113,000 


757 


758 


3564.582 


0.9 


-0.01 


-0.000 


3564.582 


19386,000 


757 


760 


5123.042 


0.2 


-0.89 


-0.022 


5123.020 


233,000 


757 


761 


3074.378 


0.7 


-0.83 


-0.012 


3074.366 


249,000 


758 


762 


3672.189 


0.8 


-0.66 


-0.012 


3672.177 


314,000 



Number of lengths = 116 
Maximum length =29334.857 
Minimum length = 1049.944 
Average length = 9401.455 



STATISTICS 
Maximum positive v in seconds = 1.41 
Maximum negative v in seconds = — 1 .82 
Average length v in seconds = 0.42 
Maximum positive v in meters = 0.093 



Maximum negative v in meters = 0.092 
Average length v in meters = 0.018 

The sum of pvv in seconds = 32 . 0645 

The sum of vv in seconds = 36 . 7634 



Horizontal Crnstal Movements 



263 



Table 7A.— Adjustment 1 adjusted positions of preearthquake survey stations i 





Geographic position 


Plane coordinates- 


-Zone VII 






















Latitude 


Longitude 


X 


r 




O t ft 


O t ft 


Feet 




01 


34 08 24.13923 


118 38 41 .07085 


4092459.20 


4163510.61 


02 


34 07 43.28132 


118 30 42.98600 
118 38 22.90210 


4132638.09 
4094114.19 


4159283.99 


03 


34 15 25.40070 


4206090.10 


04 


34 20 14.88075 


118 27 15.52113 


4150169.26 


4235236.24 


05 


34 17 33.37401 


118 24 19.55491 
118 27 40.66384 


4164914.46 
4148038.84 


4218895.58 


06 


34 17 21.86799 


4217748.98 


07 


34 18 19.66953 


118 25 58.17073 


4156644.60 


4223582.53 


08 


34 19 30.09478 


118 25 51.38155 


4157220.97 


4230701.26 


09 


34 17 30.02505 


118 29 14.32599 


4140181.01 


4218584.42 


10 


34 15 27.78137 


118 31 10.80743 


4130384.91 


4206243.24 


11 


34 17 14.47012 


118 32 23.72111 


4124286.36 


4217040.05 


12 


34 18 42.15189 


118 31 58.45349 


4126423.91 


4225899 . 53 


13 


34 19 12.75229 


118 33 53.40055 


4116788.41 


4229013.27 


14 


34 14 44.19042 


118 29 16.78301 


4139949.45 


4201820.71 


15 


34 15 48.73046 


118 24 26.62268 


4164313.76 


4208317.68 


16 


34 21 11.67283 


118 24 58.73696 


4161644.80 


4240965.92 


17 


34 08 13.09229 


118 19 29.67663 


4189241.55 


4162250.29 


18 


34 12 54.48156 


118 16 44.67239 


4203096.65 


4190699.39 


19 


34 09 48.84883 


118 11 45.00525 


4228288.67 


4171957.92 


20 


34 13 25.51247 


118 03 38.66826 


4269098.66 


4193941.90 


21 


34 16 08.38752 


118 14 17.09792 


4215472.01 


4210310.10 


22 


34 20 55.42361 


18 13 41 .75065 


4218408.81 


4239329.42 


23 


34 22 31.89266 


118 10 28.65164 


4234585.00 


4249102.47 


24 


34 22 54.69144 


18 02 01.25939 


4277109.53 


4251502.70 


25 


34 22 54.69144 


18 02 01.25939 


4277109.53 


4251502.70 


26 


34 30 06.10342 


118 06 02.79556 


4256765.35 


4295062.54 


27 


34 23 12.65722 


18 11 01.76593 


4231803.21 


4253219.23 


28 


34 31 50.26668 


18 08 50.24810 


4242730.65 


4305564 . 1 7 


29 


34 32 51.69901 


18 12 52.65572 


4222441.22 


4311744.44 


30 


34 27 35.29551 


118 13 04.37995 


4221496.63 


4279756.64 


31 


34 23 10.27034 


18 19 02.70009 


4191495.06 


4252945 . 28 


32 


34 23 10.87195 


18 19 43.79059 


4188051 .14 


4253005 . 75 


33 


34 33 37.91250 ] 


18 21 18.25320 


4180147.46 


4316396.35 


34 


34 33 39 . 50083 


18 21 18.46343 


4180129.91 


4316556.93 


35 


34 35 58.91097 


18 23 49.57945 


4167499.39 


4330656.15 


36 


34 34 01.28886 


18 24 42.65223 


4163053.28 


4318768.01 


37 


34 35 54 . 58443 


18 27 08.85071 


4150839.50 


4330233.67 


38 


34 33 24.32169 


18 28 11.79036 


4145557.25 


4315049.20 


39 


34 35 11.66816 


18 31 22.10029 


4129659.11 


4325926.97 


40 


34 32 44.06939 


18 29 56.70543 


4136775.13 


4310992.85 


41 


34 32 00.68913 1 


18 32 17.12216 


4125019.77 


4306628.62 


42 


34 31 02.84812 ] 


18 30 52.32614 


4132104.01 


4300767.77 


43 


34 29 52 . 1 7062 


18 33 00.98563 


4121322.24 


4293643.66 


44 


34 29 29.16713 


18 31 03.90903 


4131117.62 


4291298.87 


45 


34 28 45.12452 


18 33 56.59210 


4116652.43 


4286875.95 


46 


34 27 45.55887 


18 32 23.73840 


4124414.01 


4280837 . 53 


47 


34 27 50.60574 


18 34 21.38292 


4114564.01 


4281369.25 


48 


34 26 15.70703 


18 32 31.66863 


4123731.38 


4271755.49 


49 


34 25 46.76276 


18 34 47.40713 


4112354.62 


4268854.80 


50 


34 24 58.91571 


18 32 21.39086 


4124576.61 


4263990.73 


51 


34 23 38.46348 I 


18 34 56.13016 


4111592.27 


4255886.55 


52 


34 23 39.28902 


18 32 04.87432 


4125944.53 


4255938.36 


53 


34 21 21.89022 


18 35 24.06567 


4109216.42 


4242086.03 


54 


34 20 39.20798 1 


18 31 11.00075 


4130426.16 


4237725.21 


55 


34 22 30.95957 1 


18 32 06.97026 


4125755.22 


4249031.19 


56 


34 21 08.05753 


18 25 43.10223 


4157924.63 


4240603 . 70 


57 


34 19 47.20988 


18 36 00.20030 


4106161.80 


4232522.54 


58 


34 19 49.65055 


18 36 00.57029 


4106131.41 


4232769.35 


59 


34 31 57.060.% 1 


18 28 39.91917 


4143191.96 


4306230.71 


60 


34 29 46.72421 1 


18 40 03.80289 


4085929 . 74 


4293188.62 


61 


34 34 02.75797 1 


18 44 30.62807 


4063699.15 


4319153.53 


62 




18 44 30.86595 


4063679.42 


4319193.70 


63 


34 35 43.93793 1 


18 34 43.89374 


4112794.13 


4329225.29 


64 


34 41 35.33648 1 


18 33 37.72068 


4118405.61 


4364738.39 



1 The geographic position of station Cahuenga 2, No. 17, is adjusted to North American Datum of 1927. All other stations depend on this 
position. 



2M 



San Fernando Earthquake <>\ 1971 



Table 7 B.— Adjustment I adjusted potUumt «\ postearthquake %uri < 



raphii po Plane coordinai / • VII 

Station ninnlx r 

Latitude Longitude X Y 

' " " ' " Feet 

701 34 08 24 14020 1 1!! 38 41 ,0791 I 4092456 SO 4163510 71 

702 34 07 43.64195 118 30 43.02693 4132634.71 4159320 45 

703 34 15 25.40419 118 38 22.91341 4*mil) 24 4200090 40 

704 34 20 14.87897 118 27 15.53396 4150168.18 4235236.06 

705 34 17 33 388 1 18 24 19 63760 4104907 52 421%'/? 02 

706 34 17 22 29300 118 27 40.15621 414808149 4217791 90 

707 34 18 19.67349 118 25 58.21549 4156640 4223562 

709 34 17 30.02622 118 29 14.34207 4140179 66 4218564 54 

710 34 15 27.78918 118 31 10.81176 4130384 55 4206244' 

711 34 17 14.47639 118 32 23.72981 4124285.63 4217040 

712 34 18 42.15556 118 3158.46355 4126423 07 4225899.90 

713 34 19 12 81828 118 33 51 18749 4116907 28 4229019 

715 34 15 48.74704 118 24 20 61947 4164314.03 420831'* 

717 34 08 15 09229 118 19 29 07063 4189241 55 4162250.29 

718 34 12 52.92448 1 18 10 49 68356 4202675 88 4190541 77 

719 34 09 48.84660 118 1145.00406 4228288 77 4171957 09 

720 34 13 21.28449 118 03 42 0", 4208815 V, 4191513 75 

721 34 16 08.38088 118 14 17.09381 4215472 30 4210310 04 

724 34 22 54.68992 1 18 02 01 25808 4277109 59 4201 502 

726 34 27 35.11248 118 13 04.13387 4221517.25 4279738.16 

727 34 23 12.65529 118 1101.76915 423180294 4253219 03 

729 34 32 51.69627 118 12 52.64923 4222441.76 4311744 

730 34 27 35.29071 118 13 04 37613 4221496.95 42797%. 15 

731 34 23 10.26417 118 19 02 09809 4191495.22 4252944.65 

732 34 23 10.86569 118 19 43.79137 418805107 4253005.12 

733 34 33 37.91200 118 21 18.24694 4180147.98 4316396.30 

734 34 33 39.50033 118 21 18.45717 4180130.43 4316556.88 

735 34 20 39.20911 118 31 1101028 4130425.36 4237725.33 

736 34 19 46.09310 118 35 59.05789 4100257.32 4232409.39 

737 34 19 49.65577 118 36 00.58040 4106130.57 4232769.88 

738 34 2108.04720 118 25 43.11453 4157923.60 4240602.65 

739 34 22 30.96428 118 32 06.97924 4125754.47 4249031.67 

740 34 2121.89643 118 35 24.07459 4109215.68 4242086.66 

741 34 23 39.29397 118 32 04.88375 4125943.74 4255938.86 

742 34 23 38.47045 118 34 56.13854 4111591.57 4255887.26 

743 34 24 58.92016 118 32 21.39831 4124575.98 4263991.18 

744 34 25 46.76987 118 34 47.41398 4112354.05 4268855.52 

745 34 26 19.79007 118 32 29.50673 4123913.31 4272167.89 

746 34 27 50.61142 118 34 21.38809 4114563.57 4281369.82 

747 34 27 45.56482 118 32 23.74249 4124413.67 4280838.13 

748 34 28 45.13156 118 33 56.59600 4116652.10 4286876.66 

749 34 29 29.17290 118 3103.91224 4131117.35 4291299.46 

750 34 29 52.17740 118 33 00.98803 4121322.04 4293644.34 

751 34 3102.85334 118 30 52.32809 4132103.85 4300768.30 

752 34 3157.06446 118 28 39.91392 4143192.40 4306231.11 

753 34 33 24.32593 118 28 11.78874 4145557.38 4315049.63 

754 34 32 44.07428 118 29 56.70611 4136775.07 4310993.35 

755 34 35 11.67326 118 3122.09766 4129659.34 4325927.48 

756 34 32 00.69492 118 32 17.12271 4125019.73 4306629.21 

757 34 3101.29329 118 34 57.80237 4111561.49 4300653.91 

758 34 32 35.80874 118 33 37.20888 4118327.06 4310193.22 

759 34 33 46.16172 118 32 48.70588 4122399.56 4317296.86 

760 34 30 06.68637 118 38 07.49410 4095671.17 4295176.33 

761 34 3120.21196 118 36 56.15203 4101662.91 4302592.27 

762 34 32 37.32574 118 36 01.21302 4106280.48 4310375.73 

763 34 34 40.92363 118 34 51.89194 4112109.98 4322856.36 

764 34 29 46.73712 118 40 03.80613 4085929.47 4293189.93 

765 34 34 03.16718 118 44 30.86318 4063679.65 4319194.97 

766 34 34 02.77056 118 44 30.62530 4063699.39 4319154.80 

767 34 35 43.94567 118 34 43.89125 4112794.34 4329226.07 

768 34 4135.34187 118 33 37.71039 4118406.47 4364738.93 

1 The geographic position of station Cahuenga 2, No. 717, is adjusted to North American Datum of 1927. All other stations depend on this 
position. 



Horizontal Crustal Movements 



265 



Table 8 A. —Adjustment 1 position shifts referred to station Cahnenga 2 



Station 



Postearthquake minus 


preearthquake 


Resultant 


vector 


AX 


AT 


L 


Azimuth 


Feet 


Feet 


Feel 


o 


-0.73 


+0.64 


0.97 


130 


-0.06 


+ 0.50 


0.50 


175 


-0.33 


+ 0.71 


0.78 


155 













-0.70 


+0.10 


0.71 


ioo 


-0.95 


+0.36 


1.02 


110 


-0.36 


+0.79 


0.87 


155 


+0.44 


+0.40 


0.59 


230 


-0.34 


+0.60 


0.69 


150 


-0.80 


+0.12 


0.81 


100 


-0.75 


+0.48 


0.89 


125 


+0.10 


-0.23 


0.25 


335 


+0.54 


-0.28 


0.61 


295 


+0.13 


+0.43 


0.45 


195 


-0.70 


+0.71 


1.00 


135 


-0.27 


+ 1.31 


1.34 


170 


-0.44 


+0.57 


0.72 


140 


+0.16 


-0.63 


0.65 


345 


-1.03 


-1.05 


1.47 


45 


-0.84 


+0.37 


0.92 


115 


-0.27 


-0.20 


0.34 


55 


-0.79 


+0.50 


0.93 


120 


+0.06 


-0.15 


0.16 


340 


-0.07 


-0.35 


0.36 


10 


-6.94 


+ 1 .44 


7.09 


100 


+0.27 


+ 1.68 


1.70 


190 


+0.32 


-0.48 


0.58 


325 


+0.52 


-0.05 


0.52 


275 


+0.52 


-0.05 


0.52 


275 


-0.84 


+0.53 


0.99 


120 


-0.07 


-0.63 


0.63 


5 


-0.04 


+0.59 


0.59 


175 


+0.23 


+0.51 


0.56 


205 


-1.35 


+0.12 


1.36 


95 


-0.16 


+0.53 


0.55 


165 


-0.63 


+0.45 


0.77 


125 


+0.86 


+0.54 


1.02 


240 


+0.35 


-0.06 


0.36 


280 


-0.20 


+0.68 


0.71 


165 


-1.08 


-0.18 


1.09 


80 


-3.75 


+0.40 


3.77 


95 


-0.74 


+0.63 


0.97 


130 


+0.17 


-0.14 


0.22 


310 


-0.27 


+0.59 


0.65 


155 


+0.21 


+0.78 


0.81 


195 


+0.23 


+ 1.27 


1.29 


190 


+0.24 


+ 1.27 


1.29 


190 


-0.57 


+0.72 


0.92 


140 



Bluff 

Brushy 

Bum 

Cahuenga 2 

Calabasas 

Chatsworth 

Corner 2 

Deer 

Dry 

East 

Edison 

Flint 

Hauser 

House 

Lock 

Loma Verde 

Long 

Magic 

May 

Mission Pt 

Mt. Gleason 

Newhall 

Pacifico 

Pacoima E-2 ECC 1 . . . 

Pacoima L-l 

Pacoima No. 2 

Parker 

Pelona 

Pelona ECC 2 

Pico L-9 AUX 2 ECC 1 

Port 

Powerhouse 

Red 

Reservoir 

Rock 

Saugus 

Sawmill 

Sister Elsie 

Steer 

Sylmar F-8 

Sylmar 1-12 

Towsley 

Verdugo AUX 

View 

Warm Springs 

Whitaker 

WPK A-7A AUX 1 . . 
Yucca 



266 



San Fernando Earthquake of 1971 



Table 9A.—Adjuitment I 9f-percent ruoi tlUpiet referred t» station Calwengm 2 



Axes < l-rrt) 



Station ' >in- sigma 

aj 

Bluff 19 

Bum .64 

Cahucnga 2 

Calabasas ,46 

Chatsworth .47 

Corner 2 .36 

Deer .67 

Dry .60 

East .43 

Edison .48 

Flint .21 

Hauser .68 

House .70 

Lock .55 

Long .63 

Magic .41 

May .38 

Mission Pt .41 

Mt. Gleason .46 

Newhall .51 

Pacifico .57 

Pacoima E-2 ECC 1 .32 

Pacoima L- 1 .30 

Pacoima No. 2 .26 

Parker .54 

Pelona .68 

Pelona ECC 2 .68 

Pico L-9 AUX 2 ECC 1 .49 

Port .41 

Powerhouse .70 

Red .77 

Reservoir .35 

Rock .66 

Saugus .54 

Sawmill .96 

Sister Elsie .25 

Steer .66 

Sylmar F-8 .38 

Sylmar 1-12 .33 

Towsley .51 

Verdugo AUX .17 

View .63 

Warm Springs .82 

Whitaker .91 

WPK A-7A AUX 1 .91 

Yucca .59 

t Semimajor axis. 
t Semiminor axis. 
* Angle of orientation is measured positive counterclockwise from east. 



95 pi 



bt 



at 



bj 



Of S<-f! 



21 


.25 
23 
.22 
.26 
.25 
.22 
.23 
.16 
.30 
.26 
.24 
.26 
.22 
.20 
.21 
.26 
.23 
.34 
.19 
.19 
.18 
.27 
.25 
.25 
.23 
.22 
.26 
.27 
.20 
.26 
.24 
.31 
.19 
.26 
.22 
.21 
.23 
.14 
.26 
.27 
.33 
.33 
.25 



96 

1 58 


I 12 
I .16 

.88 
1 64 
1.48 
1 .06 
1.18 

.52 
1 68 
1.72 
1.34 
1.54 
1 ,01 
93 
1 .00 
1 .12 
1 24 
1.40 

.79 

.73 

.63 
1.32 
1.67 
1.67 
1.20 
1.01 
1.72 
1.89 

.85 
1.63 
1.32 
2.36 

.61 
1.61 

.93 

.80 
1.26 

.41 
1.54 
2.00 
2.22 
2.22 
1.45 



52 
.64 


60 

r ;7 
53 

63 
.62 

.53 
.56 

40 

T', 

.59 
.63 

.55 
.49 
.52 

.65 
.57 
84 
.47 
.46 
.44 
.66 
.62 
.62 
.56 
.54 

.66 
.49 
.65 
.59 
.76 
.46 
.64 
.55 
.51 
.57 
.34 
.64 
.67 
.82 
.82 
.61 



'A 

87 

70 
62 
19 
33 
43 
41 
14 
160 
17 
45 

1 

26 

50 

152 

39 

129 

42 

28 

32 

163 

4 

4 
56 

4 
27 
22 
46 
25 
37 
22 
155 
31 
35 
33 
51 

1 
27 
27 
42 
42 
41 



Horizontal Crustal Movements 267 




765 



764 



APPARENT HORIZONTAL DISPLACEMENT 





768 



Scale for Vectors and Ellipses 
12 3 4 5 6 7 Feet 



2 Meters 




O 
718 



717 

A 
CAHUENGA 2 
( Held Fixed ) 



o 

719 




Figure 2.4. — Adjustment 1 position vectors and 95-percent error ellipses referred to station Cahuenga 2. 



268 



San Fernando Earthquake of 1071 



Table 10.— Adjustment i parameter! of itram (adjusted obit 



Triangle (stations]* 







1 '<. 


10 ■ 










Ex 


E t 


Of! 1 


■< 




P 




w 


+ 24 


+ 1 


o 

149 


24 


+ 


12 


+ 


4 


I 18 


- 9 


165 


27 




', 


— 


18 


* 10 


- 0.4 


33 


10 


+ 




— 


4 


f 28 


- 11 


113 




+ 


B 




20 


{ 42 


- 41 


156 


83 


+ 


1) 2 


— 


24 


+ 3 


-414 


S3 


41*, 


-20", 


— 




- 3 


-276 


65 


27 ; 


- 


S9 




49 


+ 182 


- 11 


1 58 


192 




86 


— 


9 


+ 3 


-420 


85 


432 


-213 


— 


48 


- 36 


-236 


49 


199 


- 


16 


- 120 


+ 1 36 


- 60 


1 59 


195 


1 






33 


+ 126 


- 50 


119 


170 




38 


+ 




- 38 


-408 


72 


421 


-248 




13 


- 20 


-306 


59 


285 


- 




+ 


72 


+201 


-444 


126 


645 


- 


22 


— 


162 


+ 188 


- 41 


157 


229 


+ 


73 


— 


24 


+227 


- 39 


58 


266 


+ 


94 


— 


94 


+ 4 


- 75 


17 


79 


— 


35 


— 




+ 9 


- 74 


134 


83 


— 


32 


— 


12 


- 5 


- 79 


124 


74 


— 


42 


— 


1 


- 12 


- 49 


123 


37 


— 


31 


+ 


14 


- 20 


- 27 


174 


7 


— 


24 


+ 


32 


+ 35 


- 89 


163 


124 


— 


27 


— 




+ 34 


- 32 


162 


66 


+ 


1 


+ 


1 


+ 5 


- 24 


163 


29 


— 


9 


+ 


4 


+ 10 


- 26 


133 


35 


— 


8 


+ 


24 


+ 26 


- 7 


120 


33 


+ 


9 


+ 


21 


+ 15 


-102 


162 


117 


— 


44 


— 


5 


+ 1 


- 2 


1 


4 


— 


1 


+ 


5 


+ 2 


+ 1 


83 


1 


+ 


2 


+ 


7 


+ 7 


- 0.1 


52 


7 


+ 


3 


+ 


4 


+ 11 


- 8 


151 


19 


+ 


2 


— 


9 


- 7 


- 11 


87 


3 


— 


9 


— 


11 


+ 71 


- 17 


11 


87 


+ 


27 


+ 


17 


- 4 


- 8 


156 


4 


— 


6 


— 


11 


+ 32 


- 7 


18 


40 


+ 


12 


— 


3 


+ 15 


- 17 


27 


32 


— 


1 


+ 


12 


+ 11 


- 6 


57 


17 


+ 


2 


— 


1 


+ 9 


- 21 


43 


30 


— 


6 


- 


5 


+ 9 


+ 3 


45 


6 


+ 


6 


+ 


4 


+ 7 


+ 1 


79 


6 


+ 


4 


+ 


6 


+ 9 


+ 1 


72 


9 


+ 


5 


+ 


7 


+ 11 


+ 2 


62 


9 


+ 


6 


+ 


6 


+ 11 


+ 2 


62 


9 


+ 


6 


+ 


6 


+ 68 


+ 8 


9 


61 


- 


38 


+ 


9 


+ 32 


+ 5 


27 


28 


+ 


19 


+ 


1 


+ 32 


+ 5 


27 


28 


+ 


19 


+ 


1 


+ 38 


+ 6 


47 


32 


+ 


22 


+ 


11 


+ 8 


- 1 


106 


9 


+ 


3 


+ 


12 


+ 18 


- 4 


85 


22 


+ 


7 


+ 


19 


+ 11 


- 9 


145 


20 


+ 


1 


+ 


2 


+ 7 


- 7 


146 


14 


— 


0.2 


+ 


5 


+ 10 


- 4 


16 


14 


+ 


3 


+ 


15 


+ 26 


- 2 


109 


28 


+ 


12 


+ 


13 


+ 19 


- 2 


104 


20 


+ 


8 


+ 


16 


+ 29 


- 47 


124 


76 


— 


9 


+ 


30 


+ 26 


- 4 


105 


30 


+ 


11 


+ 


11 


+ 20 


- 8 


114 


28 


+ 


6 


+ 


10 


+ 25 


- 23 


124 


49 


+ 


1 


+ 


21 


+ 16 


- 6 


94 


22 


+ 


5 


+ 


14 


+ 16 


- 8 


104 


25 


+ 


4 


+ 


27 


+ 11 


- 13 


126 


24 


— 


1 


+ 


19 


+ 11 


+ 6 


148 


5 


+ 


8 


-j- 


15 


+ 7 


+ 2 


35 


5 


+ 


4 


+ 


13 


+ 27 


- 24 


72 


51 


+ 


2 


— 


12 


+ 4 


- 15 


136 


20 


— 


6 


+ 


20 


+ 7 


+ 2 


36 


5 


+ 


4 


+ 


13 


+ 18 


+ 7 


80 


11 


+ 


12 


+ 


22 


+ 24 


+ 3 


65 


21 


+ 


13 


+ 


16 


+ 11 


- 6 


133 


16 


+ 


3 


+ 


2 


+ 10 


- 4 


111 


13 


+ 


3 


+ 


8 


+ 10 


- 13 


122 


22 


— 


1 


+ 


D 


+ 10 


- 8 


108 


18 


+ 


1 


+ 


9 


- 5 


- 10 


30 


5 


— 


8 


j. 


17 



701-705 70(» 

703 711 710 

703 737 711 

703 737 738 

703 738 706 

704 705 701) 

704-705 709 

704 706 70') 

704-707 700 

704 738 705 

704-738-706 

704-738-709 

705-700 738 

705-709-738 

705-715-709 

700-709-738 

706-715-717 

7()()-738-715 

709-710-711 

709-710-712 

709-711-712 

709-712-738 

709-715-710 

710-711-712 

711-737-735 

712-735-738 

715-721-717 

715-738-721 

717-718-719 

717-721-719 

718-721-719 

721-727-724 

721-731-727 

721-732-731 

721-732-727 

721-738-732 

724-727-730 

724-730-729 

727-732-730 

729-730-732 

729-730-734 

729-732-734 

730-732-733 

730-732-734 

731-732-734 

732-738-733 

732-738-734 

732-738-752 

732-752-734 

734-738-752 

734-752-755 

734-752-765 

734-755-768 

735-737-739 

735-737-740 

735-739-741 

735-740-739 

735-740-741 

735-741-738 

737-740-739 

737-752-738 

737-764-738 

737-764-752 

737-765-752 

737-765-764 

737-766-738 

737-766-752 

738-764-752 

738-766-752 

739-740-741 

739-740-742 

739-742-741 

740-742-741 

741-742-743 

See footnotes at end of table 



Horizontal Crustal Movements 



269 



Table 10.— Adjustment 1 parameters of strain (adjusted observations)— Continued 



Triangle (stations)* 



Ex 



Units X 10" 6 



0e\ 



741-742-744. 
741-744-743. 
742-744-743. 
743-744-746. 
746-748-747 . 
746-752-747. 
746-764-748. 
746-764-752. 
746-766-747 . 
746-766-752 . 
747-748-749. 
747-748-750. 
747-750-749. 
747-750-752 . 
747-766-752. 
748-750-749. 
749-750-751. 
749-750-756. 
749-756-751. 
750-754-751. 
750-754-752. 
750-756-751 . 
750-756-752 . 
750-756-754. 
751-754-752. 
751-755-754. 
751-756-754. 
751-756-755. 
752-754-753. 
752-754-755. 
752-755-753. 
752-756-754. 
752-756-755. 
752-764-755. 
752-764-765. 
752-764-767. 
752-765-767. 
752-767-755. 
753-754-755. 
754-756-755. 
755-764-767. 
755-764-768. 
755-767-768. 
764-765-767. 
764-768-767. 



+ 


2 


+ 


4 


+ 


6 


+ 


4 


+ 


29 


+ 


17 


+ 


31 


+ 


17 


+ 


38 


+ 


15 


+ 


7 


+ 


9 


+ 


4 


+ 


20 


+ 


12 


+ 


6 


— 


4 


— 


2 


— 


5 


+ 


6 


+ 


61 


+ 


2 


+ 


27 


— 


2 


+ 


68 


+ 


11 


+ 


1 


— 





+ 


59 


+ 149 


+ 


10 


— 


82 


+ 


27 


+ 


16 


+ 


8 


+ 


13 


+ 


11 


+ 


11 


+ 


15 


+ 


0. 


— 


6 


+ 


5 


— 


2 


— 


3 



- 0.2 



— 


7 


— 


11 


— 


5 


— 


12 


+ 


5 


— 


15 


+ 


2 


+ 


4 


— 


2 


— 


3 


+ 


1 


+ 


3 


— 


5 


+ 


3 


— 


5 


— 


7 


— 


6 


— 


6 


— 


7 


— 


5 


— 


9 


+ 


8 


— 


4 


— 


11 


— 


1 


— 


6 


— 


7 


— 


6 


— 


9 


— 


17 


— 


32 


+ 


18 


— 


2 


— 


8 


— 


14 


— 


5 


— 


7 


— 


18 


— 


7 


— 


10 


+ 


0.4 


— 


4 


— 


4 


— 


11 


— 


10 



104 

168 

128 

148 

61 

25 

84 

68 

54 

42 

120 

8 

85 

2 

33 

54 

29 

44 

95 

106 

157 

64 

175 

51 

166 

65 

73 

59 

151 

11 

113 

141 

177 

158 

16 

163 

133 

140 

27 

59 

158 

5 

2 

29 

61 



9 

15 

12 

16 

24 

33 

29 

13 

40 

17 

6 

6 

9 

17 

16 

13 

2 

3 

2 

10 

70 

3 

31 

9 

69 

14 

9 

6 

68 

166 

43 

84 

28 

24 

23 

18 

19 

29 

22 

10 

8 

3 

9 

9 

7 



2 

4 

1 

4 

17 

1 

16 

11 



+ 
+ 



+ 18 

+ 6 
+ 4 
+ 6 

- 0.3 
11 

3 
0.3 

- 5 

- 4 

- 6 
+ 0.5 
+ 26 

- 5 
+ 11 

- 6 
+ 33 

- 6 

- 3 

- 3 
+ 25 
+ 66 

- 11 
16 
12 

4 



+ 
+ 
+ 



+ 

+ 

+ 
+ 
+ 



+ 13 

+ 23 

+ 16 

+ 18 

+ 6 

+ 10 

+ 16 

+ 24 

+ 15 

+ 19 

+ 7 

+ 12 

+ 9 

+ 15 

+ 18 

+ 15 

+ 11 

+ 12 

+ 12 

+ 14 

- 11 
+ 13 
+ 8 
+ 10 

- 3 
+ 9 
+ 10 
+ 12 

- 18 
+ 55 

- 13 

- 31 
+ 9 
+ 6 
+ 19 
+ 10 
+ 1 
+ 3 
+ 16 
+ 11 
+ 14 
+ 16 
+ 17 
+ 12 
+ 17 



* Stations are identified by postearthquake station numbers. 
Ei, E2 Principal axes of strain. 

6 Direction of Ei principal axis of strain measured positive 
counterclockwise from east. 



7 Total shear 7= V7J + 7I. 

p Dilatation — positive for expansion, negative for contraction. 

u Rotation positive clockwise. 



270 San Fernando Earthquake of 1971 



MAXIMUM RIGHT LATERAL SHEAR (y) 
(OVER 50 x 10 '' Radians) 



Scale for Gamma (y) 
600 x 10 * Radians 



765/ 



753 



754 



756 



l\ 752 



751 



764 




Epicenter 
® 



738 



737 



704 



712 



711 V 



710 



709 




721 



717 

▲ 

CAHUENGA 2 

( Held Fixed ) 



Figure 3A. — Adjustment 1 maximum shear (y), showing direction and magnitude of maximum positive simple shear for triangular 

areas in which shear is greater than 50 X 10-s radians. 



Horizontal Crustal Movements 271 



RIGHT LATERAL SHEAR (y) 



Scale for Gamma (y) 

50 x 10" 6 Radians 



5 Miles 



10 Km 




• \ \ 



},V 



"7 o / '"-••?.&„ ® E P icenter 



♦ San Fernando 



717 

A 
CAHUENGA 2 
( Held Fixed ) 



Figure 3B. — Adjustment 1 maximum shear (y), showing direction and magnitude of maximum 
positive simple shear for triangular areas in which shear is less than 50 X 10-s radians. 



272 San Fernando Earthquake of 1971 



PRINCIPAL AXES OF STRAIN E,,E^ 



Scale for E,. E, 



50 x 10 * Radians 



5 Miles 



\ 



/' 



\ ^ 



{ 



\ "••■Z?* 6 , ® Epicenter 

\ 






X 



• San Fernando 



\ 



717 

A 
CAHUENGA 2 
( Held Fixed ) 



5 10 Kr 



Figure •/. — Adjustment I principal axes of strain, showing direction and magnitude of maximum (E ) and minimum (EJ 
elongation (solid line) or contraction (dashed line). Triangular areas are identical to those in figure 3B. 



Horizontal Crustal Movements 



273 



Table 5C— Adjustment 2 corrections to preearthquake observed horizontal directions 





Station 


\* 




Station 






Station 






Station 














V 






v" 






V 


From 


To 




From 


To 




From 


To 




From 


To 




1 






12 






21 






32 








2 


-0.24 




13 


0.82 




15 


-0.11 




31 


1.46 




3 


-0.45 




54 


-0.21 




16 


-0.82 




33 


0.29 




14 


0.85 




56 


-0.84 




17 


-0.59 




56 


-0.95 




57 


-0.15 


13 








18 


-0.09 




59 


-0.14 


2 








11 


0.55 




19 


0.37 


33 








1 


0.76 




12 


-0.63 




20 


0.59 




27 


-0.43 




3 


0.09 




54 


-0.12 




22 


-0.64 




29 


-1.00 




14 


1 .03 




57 


0.20 




23 


0.50 




30 


-0.87 




15 


-0.05 


14 








31 


0.08 




32 


0.81 




16 


-0.07 




1 


-0.47 




56 


0.71 




56 


0.88 




17 


-1 .03 




2 


0.36 


22 








59 


0.61 




18 


0.12 




3 


-0.58 




21 


0.28 


34 








57 


-0.86 




5 


0.29 




23 


0.56 




26 


-0.67 


3 








6 


0.46 




31 


-0.84 




30 


-0.23 




1 


-0.35 




15 


0.11 


23 








31 


-1.28 




2 


— 0.22 




16 


0.96 




20 


-0.31 




35 


0.51 




14 


0.90 




17 


-1.10 




21 


-0.33 




36 


0.41 




16 


-0.21 




57 


-0.04 




22 


-0.81 




39 


0.21 




57 


-0.14 


15 








24 


0.65 




56 


0.74 


4 








2 


0.20 




26 


0.65 




60 


-0.07 




5 


-0.08 




4 


0.03 




30 


0.02 




64 


0.36 




6 


0.02 




5 


— 0.11 




31 


0.13 


35 








7 


0.29 




6 


— 0. 16 


24 








34 


-1.13 




8 


-0. 10 




9 


0.86 




20 


-0.55 




36 


-0.24 




15 


-0. 11 




14 


-0.34 




23 


-0.72 




37 


0.19 


5 








16 


— 0.84 




26 


1.27 




38 


1.31 




4 


0.25 




17 


— 0.32 


25 








39 


0.29 




6 


0.04 




18 


0.04 




27 


-0.74 




64 


-0.43 




7 


— 0. 19 




21 


0.87 




28 


0.23 


36 








8 


0.02 




56 


— 0.05 




29 


0.51 




34 


-0.01 




14 


— 0. 18 




57 


-0.20 


26 








35 


-0.04 




15 


0.08 


16 








23 


-0.71 




37 


0.45 


6 


4 


0.37 




2 

3 

6 

9 

14 

15 

17 

18 

21 

56 


-0.19 

0.15 

0.10 

1.10 

-0.11 

-0.80 

-0.55 

-0.70 

0.39 

0.22 




24 
30 


-1.01 
0.48 


37 


38 


-0.40 




5 

7 


0.05 
-0.34 




27 


34 


1.25 




35 
36 


-0.75 
0.10 




8 

9 

14 

15 

16 


-0.27 
0.29 
0.00 
0.04 

-0.08 






25 
28 
29 
30 
32 


-0.03 
0.33 

-0.20 
0.60 

-0.37 


38 


38 
39 
40 

35 


0.24 
0.31 
0.10 

0.06 


_ 


56 


-0.03 






33 


-0.33 




36 


0.29 


7 


4 


-0.85 


17 


57 


0.36 


28 


27 


0.04 




37 
39 


-0.46 
-0.07 




5 


0.04 








29 


-0.15 




40 


0.19 




6 


0.42 




2 


1 .00 




30 


0.13 


39 






H 


8 


0.40 




14 
15 


-0.01 
-0.27 


29 


25 


-1.15 




34 
35 


-1.00 
-0.27 




4 


0.30 




16 


— . 49 




27 


-1.05 




37 


-0.30 




5 


0.10 




18 


— 0.38 




28 


0.31 




38 


0.04 


9 


6 

7 


-0.21 
-0.17 




19 
20 
21 


0.54 

0.00 

-0.39 




30 
32 
33 


0.90 
0.41 
0.57 




40 
41 
42 


1.02 

0.41 

-0.37 




6 


-0.36 


18 






30 








56 


-0.56 




10 


-0.39 




2 


-0.51 




23 


-0.13 




60 


0.01 




11 


0.54 




15 


-0.11 




26 


-0.65 




63 


1.03 




12 


0.15 




16 


-0.07 




27 


0.02 




64 


0.00 




15 


0.30 




17 


0.50 




28 


-0.45 


40 








16 


0.37 




19 


-0.55 




29 


0.59 




37 


— 0.39 


10 


56 


-0.61 




20 
21 


0.79 
0.01 




31 
32 


-0.22 
0.65 




38 

39 


0.17 
-0.22 




9 


-0.01 




56 


-0.06 




33 


0.16 




41 


0.09 




11 


-0.65 


19 








34 


0.03 




42 


0.35 




12 


0.66 




17 


1.22 


31 






41 






11 








18 


-0.31 




21 


-0.53 




39 


-0.47 




9 


0.07 




20 


-0.66 




22 


0.51 




40 


-0.40 




10 


-0.09 




21 


-0.26 




23 


0.24 




42 


0.38 




12 


-0.49 


20 








30 


0.48 




43 


-0.12 




13 


0.94 




17 


0.03 




32 


-1.58 




44 


0.61 




56 


0.93 




18 


-0.15 




34 


-0.99 


42 








57 


-1.35 




19 


0.40 




56 


1 .86 




39 


-0.18 


12 








21 


-0.62 


32 








40 


0.33 




9 


0.00 




23 


0.30 




27 


-0.27 




41 


-0.12 




10 


0.81 




24 


0.51 




29 


-0.03 




43 


-0.14 




11 


-0.59 




57 


-0.47 




30 


-0.39 




44 


0.10 



27 1 San Fernando Earthquake of 1971 







Table fC. 


—Adjtutnunl 2 correction* 


in preea\ 


• llllflllllli II 


bierved hori onUtl dirertioru 


f null 


tun it 






Station 


..» 




Station 


v" 




Station 


v" 












V 
















From 


To 




l rom 


To 




1 rom 


I i 






To 




43 






50 




















41 


-0.13 




47 


Q 13 




9 


-i, 










42 


14 




48 


o 18 




11 


19 


%', 








44 


0.00 




49 


09 




12 


03 






-( 




45 


-0.22 




51 


ii 04 




15 


1 24 






-' 




46 


0.21 




52 


01 




16 


-0 47 






- j 


44 






51 








18 


-0.14 






11 




41 


-0.80 




49 


-0.22 




21 


-0 19 




61 






42 


0.39 




JO 


0.25 




11 


0.41 










43 


-0.30 




52 


-ii 10 




12 


-0 31 


60 








45 


0.67 




53 


06 




13 


Yi 


57 

04 


-1 

48 
-0 JO 

-1 
-0 90 


45 


46 
43 


0.05 

-0.17 


52 


55 

49 


19 
0.72 




39 

52 


ii 16 

-0 94 

96 






44 


-0.32 




50 


0.18 




54 


l) 63 






46 


0.05 




-.1 


41 




'.7 


0.20 






47 


-0.13 




53 


oo 




58 


- 1 66 






48 


0.57 




54 


-0.18 




59 


-0.38 




46 








55 


ii 12 




60 


-0.80 


61 








43 


0.19 




56 


-i) 85 




61 


1 .10 






-0 80 




44 


0.35 




57 


-ii 62 




04 


-0.4', 






0.25 




45 


-0.32 


53 






57 










40 




47 


-0.24 




51 


. 03 




1 


-2.05 






14 




48 


0.02 




52 


-0.59 




2 


-1 55 


i,2 






47 








54 


0.85 




3 


(i Vi 




34 


-0.75 




45 


-0.12 




55 


12 




11 


-0.32 




57 


1 39 




46 


0.49 




57 


-0.41 




13 


1.54 




59 


0.21 




48 


-0.24 


54 








14 


-d 






-0.88 




49 


-0.54 




12 


-0.26 




15 


-1.34 




63 


0.03 




50 


0.40 




13 


1.51 




It. 


-0 


S3 






48 








52 


-0.08 




20 


-0. 10 




39 


19 




45 


-0.12 




53 


-0.54 




52 


0.91 




58 


-0.90 




46 


0.35 




55 


-0.42 




53 


0.24 




59 


-1 13 




47 


-0.13 




56 


0.64 




54 


08 




60 


1.06 




49 


-0.23 




57 


-0.85 




55 


0.82 




62 


-0.53 




50 


0.14 


55 








56 


0.09 




64 


1 31 


49 








51 


-u 62 




59 


1 .36 


64 








47 


0.23 




52 


ii 00 




60 


-0.10 




34 


0.08 




48 


0.43 




53 


-0.08 




62 


1 .76 




35 


-1.20 




50 


-0.35 




54 


0.58 


58 








39 


0.27 




51 


0.08 




57 


0.13 




56 


-0.52 




56 


— 0.51 




52 


-0.71 


56 








59 


0.08 




60 


0.43 




56 


0.41 




6 


0.58 




61 


0.21 




63 


0.94 



Horizontal Crustal Movements 



275 



Table 5D.— Adjustment 2 corrections to postearthquake observed horizontal directions 





Station 


v" 




Station 


V 




Station 


v" 




Station 




From 


To 


From 


To 


From 


To 


From 


To 


V 


701 






719 






735 






746 








702 


-0.18 




717 


-0.95 




737 


-0.25 




747 


-0.05 




703 


0.84 




718 


-0.21 




738 


-0.47 




748 


0.26 




706 


-0.66 




720 


0.37 




739 


-0.21 




752 


0.59 


702 








721 


0.78 




740 


-0.34 




757 


0.16 




701 


0.23 


720 








741 


0.05 




764 


0.24 




703 


0.34 




719 


-0.52 


736 








766 


-1.18 




706 


-0.55 




721 


0.33 




703 


-0.54 


747 








715 


-0.54 




724 


0.19 




710 


1.14 




745 


-0.95 




717 


0.52 


721 








713 


1.02 




746 


-0.61 


703 








715 


-1.97 




717 


-0.45 




748 


-0.03 




701 


1.53 




717 


-0.35 




735 


0.17 




749 


1.82 




702 


-0.36 




719 


0.55 




738 


- 1 . 34 




750 


0.06 




706 


-0.62 




720 


-0.18 


737 








752 


-0.69 




736 


0.32 




724 


0.38 




713 


0.97 




766 


0.43 




738 


-0.86 




727 


-0.70 




735 


0.05 


748 






704 








731 


0.94 




738 


-0.27 




745 


-0.03 




705 


0.08 




732 


1.07 




739 


0.78 




746 


-0.04 




706 


0.18 




738 


0.25 




740 


-0.76 




747 


0.19 




709 


-0.11 


724 








752 


-0.36 




749 


-0.47 




738 


-0.16 




720 


-0.02 




764 


0.13 




750 


0.07 


705 








721 


0.33 




765 


-0.27 




757 


0.31 




704 


0.34 




726 


-0.57 




766 


-0.28 




764 


-0.03 




706 


0.06 




727 


-0.04 


738 






749 








709 


0.27 




729 


0.29 




703 


0.72 




747 


-0.72 




738 


-0.67 


726 








704 


-0.03 




748 


0.46 


706 








724 


0.34 




705 


0.17 




750 


-0.05 




701 


1.21 




727 


0.40 




706 


-0.41 




751 


0.60 




702 


1.04 




729 


-0.34 




709 


-0.37 




756 


-0.28 




703 


1.28 




732 


-0.41 




710 


-0.55 


750 








704 


-0.56 


727 








712 


1.23 




747 


0.01 




705 


-1.24 




721 


0.31 




715 


0.92 




748 


-0.09 




709 


-1.03 




724 


1.40 




721 


0.23 




749 


-0.43 




715 


-0.54 




726 


-0.60 




732 


-0.07 




751 


-0.38 




717 


0.88 




732 


-1.12 




733 


-0.88 




752 


0.43 




738 


-1.04 


729 








734 


-2.20 




754 


0.29 


709 








724 


-0.92 




735 


0.65 




756 


0.13 




704 


0.44 




726 


0.05 




736 


0.58 




757 


0.05 




705 


0.61 




730 


0.04 




737 


-0.10 


751 








706 


0.08 




732 


1.05 




741 


1.27 




749 


0.03 




711 


-1.54 




734 


-0.22 




752 


-0.11 




750 


-0.27 




712 


0.08 


730 








764 


-0.98 




754 


-0.29 




738 


0.35 




729 


-0.33 




766 


-0.04 




755 


0.45 


711 








732 


-0.20 


739 








756 


0.10 




709 


0.34 




733 


0.28 




735 


0.28 


752 








710 


0.50 




734 


0.26 




737 


-0.95 




732 


-0.06 




712 


-0.01 


731 








740 


-0.11 




734 


-0.46 




713 


-0.85 




732 


0.29 




741 


0.23 




737 


0.36 


712 








734 


-0.28 




742 


0.55 




738 


0.43 




709 


-0.10 


732 






741 








746 


-0.37 




710 


-0.93 




721 


1.31 




735 


0.56 




747 


-0.24 




711 


0.77 




726 


-0.19 




738 


-0.51 




750 


1.02 




713 


-0.14 




727 


0.50 




739 


-0.58 




753 


0.53 




735 


0.20 




729 


0.43 




740 


-0.39 




754 


-0.07 




738 


0.18 




730 


-0.20 




742 


0.54 




755 


1.22 


713 








731 


-0.31 




743 


0.36 




756 


-1.29 




711 


1.51 




733 


-1.60 




744 


0.01 




764 


-1.37 




712 


-0.10 




734 


-1.42 


743 








765 


-0.79 




735 


0.36 




738 


0.78 




741 


-0.69 




766 


2.03 




736 


0.05 




752 


0.70 




742 


-0.07 




767 


-0.94 




737 


-1.83 


733 








744 


-0.42 


753 






715 








729 


-0.83 




745 


0.35 




752 


-0.22 




702 


-0.36 




730 


-0.08 




746 


0.83 




754 


-0.31 




706 


-0.67 




732 


0.31 


744 








755 


0.51 




717 


0.91 




738 


0.60 




741 


-0.63 


754 








721 


-0.18 


734 








742 


0.37 




750 


0.09 




738 


0.31 




729 


0.53 




743 


-0.39 




751 


0.28 


717 








730 


0.51 




745 


0.28 




752 


0.18 




702 


0.44 




731 


1.37 




746 


0.36 




753 


-0.08 




706 


0.42 




732 


-0.39 


745 








755 


0.29 




715 


-0.38 




738 


-0.55 




743 


-0.78 




756 


-0.58 




718 


0.28 




752 


-0.13 




744 


0.41 




759 


-0.20 




719 


-1.18 




755 


0.48 




746 


0.06 


755 








721 


0.42 




765 


-1.10 




747 


0.61 




734 


-0.34 




736 


-0.01 




768 


-0.73 




748 


-0.30 




751 


-0.27 


718 






735 






746 








752 


0.31 




717 


0.25 




712 


0.48 




743 


0.97 




753 


0.11 




719 


-0.58 




713 


-0.06 




744 


-0.84 




754 


0.40 




721 


0.33 




736 


0.80 




745 


-0.14 




756 


-0.19 



276 San Fernando Earthquake of 1071 



Tabic 5/).— Adjustment 2 correction! to posUarthqualu oburved HorkumUii dire<iion\-(.»ntinurd 



Station 



From 



755 



751, 



757 



To 



759 
7(,4 
767 
768 

74') 
750 
751 
752 
754 
755 
757 
758 
759 

746 

748 
750 
756 
758 
760 
761 
762 
764 
767 



Station 



03 
-0.26 

0.41 
-0.17 

0.60 

-0.08 

0.35 

0.48 
. 52 
- 1 . 88 
-0.36 
0.19 
0.17 

-0.04 
-1.07 
-0.18 
-0.32 
0.27 
0.05 

0:34 

•0.22 

•0.28 

1 42 



From 



758 



759 



760 



761 



762 



To 



750 
757 
759 
762 
763 

754 
755 
756 
758 
762 
763 
767 

757 
761 

767 

757 
760 
762 
764 
767 

757 






15 


1 


05 


0.01 





1 1 


1 


,01 





67 





2\ 





>}■,', 





08 


0.09 





r,', 





39 





1 5 





04 





07 





92 





00 





37 





7! 





17 



Station 



Prom 



762 



763 



704 



765 



To 



-0.17 



758 
75') 
761 

70', 

758 

750 
762 
767 

737 

7 58 
746 
748 
752 
755 
757 
761 
765 
767 
768 



734 

737 
738 



40 
-0 20 

01 
-0 05 

-0 66 

-0 71 
77 
62 

20 

1 00 
-0 07 

15 
',7 
07 
0.12 

-2.17 
0.28 
0.85 

-0 00 



0.28 
1.53 
0.50 






From 



765 



7M, 



707 



768 



To 







764 




767 


-0 25 




1 26 




-0 21 


746 


-1 79 


747 




752 


-0 09 



752 
755 
757 

760 
761 

768 

734 
755 
764 

767 



41 

03 

-0.55 

-0 13 

-0 16 

-1 12 

-0 15 

0.82 

45 

41 

14 

12 

0.29 

-0.55 



Table 6C— Adjustment 2 corrections to preearthquake observed lengths (v's) in meters 





Station 




Observed 


Weight 


v in 


V 


in 


Adjusted 












length 


factor 


seconds 


meters 


length 


1 part in 








From 




To 






















1 




3 

17 
56 


12988 

29502 

1139 


206 
131 
270 


1.0 

1.0 
0.3 


0.60 

1.37 
1.29 








.038 

196 

.007 


1 2988 

29502 

1139 


327 
.277 


343,000 
151,000 
160,000 


1 




16 




31 




32 


1049 


944 


0.1 


-12.44 


-0 


.063 


1049 


881 


17 


,000 


31 




34 


19695 


796 


2.4 


-0.26 


-0.025 


19695 


771 


784 


,000 


34 




64 


23866 


161 


2.4 


0.58 





.067 


23866 


228 


358 


,000 


39 




63 


5237 . 


752 


0.6 


0.19 





005 


5237 


757 


1096 


,000 


60 




63 


13700.048 


1.6 


-0.47 


-0 


031 


13700 


017 


441 


,000 












STATISTICS 















Number of lengths = 8 

Maximum length = 29502 .131 
Minimum length = 1049.944 
Average length = 1 3397 . 4 1 3 



Maximum positive v in seconds = 1 .37 
Maximum negative v in seconds = — 12.44 
Average length v in seconds = 2.15 

Maximum positive v in meters = 0. 196 



Maximum negative v in meters = —0.063 

Average length v in meters = 0.054 

The sum of pvv in seconds = 6.8170 

The sum of vv in seconds =159.3183 



Horizontal Crustal Movements 



211 



Table 6D.— Adjustment 2 corrections to postearthqnake observed lengths (v's) in meters 



Station 



To 



Observed 
length 



Weight 
factor 



v in 
seconds 



v in 
meters 



Adjusted 
length 



1 part in 



702 


12312.320 


1.0 


-0.23 


-0.014 


12312.306 


901 


000 


703 


12988.248 


1.0 


-0.07 


-0.004 


12988.244 


3113 


000 


706 


23689.237 


1.0 


0.54 


0.062 


23689.299 


380 


000 


703 


18468.538 


1.0 


-0.37 


-0.033 


18468.505 


558 


000 


706 


18433.678 


1.0 


0.72 


0.064 


18433.742 


287 


000 


715 


17784.643 


1.0 


0.28 


0.024 


17784.667 


743 


000 


717 


17277.090 


1.0 


-0.61 


-0.051 


17277.039 


337 


000 


736 


8834.865 


1.0 


0.73 


0.031 


8834.896 


281 


000 


705 


6707.119 


1.2 


0.43 


0.014 


6707.133 


475 


000 


706 


5354.937 


0.8 


-0.01 


-0.000 


5354.937 


20856 


000 


707 


4063.040 


0.6 


0.01 


0.000 


4063.040 


27911 


000 


709 


5918.553 


0.8 


-0.49 


-0.014 


5918.539 


418 


000 


738 


2874.647 


0.4 


-0.46 


-0.006 


2874.641 


449 


000 


706 


5139.684 


0.8 


-0.04 


-0.001 


5139.683 


4780 


000 


709 


7537.743 


1.2 


-0.37 


-0.013 


7537.730 


562 


000 


738 


6949.956 


0.7 


0.38 


0.013 


6949.969 


543 


000 


707 


3149.940 


0.8 


-0.01 


-0.000 


3149.940 


21352 


000 


709 


2420.603 


0.7 


-1.69 


-0.020 


2420.583 


122 


000 


715 


5728.547 


1.0 


-0.02 


-0.001 


5728.546 


10417 


000 


738 


7572.380 


0.7 


-0.58 


-0.021 


7572.359 


353 


000 


711 


4867.378 


0.9 


-1.61 


-0.038 


4867 . 340 


128 


000 


712 


4749.053 


0.6 


-0.84 


-0.019 


4749.034 


245 


000 


738 


8619.200 


0.7 


0.10 


0.004 


8619.204 


2055 


000 


711 


3779.620 


0.7 


0.07 


0.001 


3779.621 


3068 


000 


712 


6111.645 


0.7 


-0.17 


-0.005 


6111.640 


1203 


000 


736 


10848.427 


0.8 


-1.23 


-0.065 


10848.362 


168 


000 


738 


13421.494 


1.0 


-1.25 


-0.081 


13421.413 


165 


000 


712 


2777.813 


0.5 


-1.49 


-0.020 


2777.793 


139 


000 


713 


4280.273 


0.5 


-0.74 


-0.015 


4280 . 258 


278 


000 


713 


3037.845 


0.6 


0.09 


0.001 


3037.846 


2366 


000 


735 


3805.260 


0.7 


0.06 


0.001 


3805.261 


3710 


000 


738 


10595.807 


1.1 


-0.40 


-0.021 


10595.786 


512 


000 


735 


4888.063 


0.7 


-0.16 


-0.004 


4888.059 


1310 


000 


737 


3492.387 


0.7 


-0.67 


-0.011 


3492 . 376 


309 


000 


738 


10030.937 


1.0 


0.84 


0.041 


10030.978 


247 


000 


718 


9546.200 


1.1 


0.40 


0.018 


9546.218 


521 


000 


721 


7177.706 


0.8 


-0.26 


-0.009 


7177.697 


799 


000 


720 


13991.396 


0.9 


0.37 


0.025 


13991.421 


555 


000 


724 


17855.019 


1.4 


0.12 


0.010 


17855.029 


1716 


000 


727 


13993.997 


1.3 


-0.44 


-0.030 


13993.967 


465 


000 


732 


15466.399 


1.6 


0.49 


0.037 


15466.436 


421 


000 


738 


19822.690 


1.5 


-0.04 


-0.004 


19822.686 


4797 


000 


730 


19012.978 


1.2 


-0.62 


-0.057 


19012.921 


333 


000 


730 


8677.040 


0.8 


1.64 


0.069 


8677.109 


126 


000 


732 


13335.795 


1.0 


-0.29 


-0.019 


13335.776 


718 


000 


730 


9754.135 


1.1 


0.22 


0.010 


9754.145 


950 


000 


732 


20746.517 


1.8 


-0.27 


-0.027 


20746.490 


774 


000 


734 


12979.516 


1.5 


-0.34 


-0.021 


12979.495 


609 


000 


732 


13054.013 


1.4 


-0.07 


-0.005 


13054.008 


2862 


000 


734 


16875.648 


1.5 


0.61 


0.050 


16875.698 


339 


000 


732 


1049.944 


0.4 


-0.06 


-0.000 


1049.944 


3181 


000 


734 


19695.934 


1.8 


0.30 


0.029 


19695.963 


682 


000 


734 


19520.397 


1.8 


-0.01 


-0.001 


19520.396 


21221 


000 


738 


9930.636 


1.2 


-1.77 


-0.085 


9930.551 


116 


000 


752 


21216.619 


1.5 


-0.79 


-0.082 


21216.537 


260 


000 


738 


24074.486 


1.7 


0.42 


0.049 


24074.535 


488 


000 


738 


24119.961 


1.7 


0.36 


0.042 


24120.003 


572 


000 


752 


11690.213 


1.2 


-0.60 


-0.034 


11690.179 


341 


000 


755 


15646.220 


1.5 


0.12 


0.009 


15646.229 


1708 


000 


768 


23866.176 


1.8 


0.45 


0.052 


23866.228 


461 


000 


737 


7557.594 


0.9 


-0.58 


-0.021 


7557.573 


354 


000 


738 


8427.302 


0.9 


-0.87 


-0.036 


8427.266 


237 


000 


739 


3728.717 


0.6 


-1.27 


-0.023 


3728.694 


163 


000 


740 


6600.029 


1.0 


-0.53 


-0.017 


6600.012 


392 


000 


741 


5717.114 


0.9 


-0.37 


-0.010 


5717.104 


551 


000 


738 


15944.742 


1.7 


0.24 


0.018 


15944.760 


862 


000 


738 


15966.080 


1.7 


0.49 


0.038 


15966.118 


419 


000 


739 


7768.221 


0.8 


-0.07 


-0.003 


7768.218 


2854 


000 


740 


2991.420 


0.6 


-0.46 


-0.007 


2991.413 


444 


000 


752 


25079.104 


1.9 


0.72 


0.088 


25079.192 


285 


000 


766 


29334.857 


1.0 


0.28 


0.039 


29334.896 


745 


000 


741 


10810.436 


0.9 


-0.78 


-0.041 


10810.395 


264 


000 


752 


20501.246 


1.8 


0.46 


0.046 


20501.292 


450 


000 


764 


27174.347 


1.6 


0.33 


0.043 


27174.390 


633 


000 


740 


5467.488 


0.7 


-0.65 


-0.017 


5467.471 


317 


000 


741 


2106.121 


0.6 


-0.96 


-0.010 


2106.111 


215 


000 


742 


4796.027 


1.0 


-0.51 


-0.012 


4796.015 


401 


000 


741 


6620.000 


0.8 


-1.25 


-0.040 


6619.960 


164 


000 


742 


4268.324 


0.6 


-0.01 


-0.000 


4268.324 


40845 


000 



278 San Fernando Earthquake of 1971 



Table 6D.— Adjustment 2 correcttotu (o pnHtarthquake ob\erved Un%tht (i/t) in metert—f^oir 



Station 



From 



To 



Observed 
length 



Weigh! 

factor 



v in 
seconds 



v in 
rn<-trrs 



Adj 
length 



1 part in 



741. 
741. 
741. 
742. 
742. 
743. 
743. 
743. 
744. 
744. 
745. 
745. 
745. 
746. 
746. 
746. 
746. 
746. 
746. 
747. 
747. 
747. 
748. 
748. 
748. 
750. 
750. 
752. 
752. 
754. 
755. 
756. 
756. 
757. 
757. 
757. 
758. 



742 


4374 


o 9 


0.18 


u <m 


4374 


1127.000 


743 


2489.515 


0.7 


-0 47 


-0 006 


2489 509 


43; 


744 


5714.684 


1.2 


-0.64 


-0 018 


5714 666 


000 


743 


4665.227 


0.9 


0.14 


003 


4V, 5 230 


1448. '//J 


744 


3959.540 


0.8 


97 


0.019 




213,000 


744 


4009.449 


1 .0 


i) 46 


0.009 


4009 458 


452,000 


745 


2500.442 


6 


-0.53 


-0.006 


2500 4 ',6 


. 000 


746 


6113.238 


1 .1 


0.03 


0.001 


6113 239 


0710,000 


745 


3665.062 


0.8 


0.17 


0.003 


065 


1225,000 


746 


3873 . 355 


0.8 


-0.13 


-0.002 


387', 


1 590 . 000 


746 


3998.506 


0.9 


-0.74 


-0.014 


492 


27: 


747 


2647.091 


0.7 


-0.45 


-0 006 


2647 OHO 


457,000 


748 


4999.769 


0.9 


-0.35 


-0 008 


4999 761 


592 , 000 


747 


3006 .661 


0.8 


88 


013 


3006 674 


Of JO 


748 


1795.146 


0.5 


-0.77 


-0.007 


1795 ) 39 


• 000 


752 


11557.006 


1.0 


11 


0.006 


11557 012 


1832,000 


757 


5948.545 


1.0 


V* 


0.011 


5948 .5 56 


524,000 


764 


9442.006 


1.1 


-0.00 


-0.000 


9442 006 


35,008 


766 


19312.904 


1.0 


on 


0.010 


19312 914 


1842,000 


748 


2997.346 


0.7 


1.39 


0.020 


2997 


149,000 


752 


9626.233 


0.9 


0.17 


0.008 


241 


118 


766 


21882.673 


1.0 


0.17 


0.018 


21882 691 


122 


750 


2506.212 


0.7 


0.21 


0.003 


2506.215 


1002,000 


757 


4476.773 


0.9 


-0.27 


-0.006 


4476 . 767 


761,000 


764 


9559.881 


1.2 


-0.01 


-0.000 


9559 881 


23072,000 


754 


7081.447 


1.0 


-0.26 


-0.009 


7081.438 


789,000 


757 


3662.679 


0.8 


-0.05 


-0.001 


3662.678 


4556,000 


754 


2435.725 


0.5 


0.19 


0.002 


2435.727 


1072.000 


755 


7283.864 


1.2 


0.25 


0.009 


7283.873 


836,000 


755 


5042.169 


0.7 


-0.34 


-0.008 


5042.161 


604,000 


767 


5237.757 


1.2 


-0.01 


-0.000 


5237.757 


19814,000 


757 


4488.173 


1.0 


-0.22 


-0.005 


4488.168 


955,000 


758 


2311.136 


0.6 


-1 .83 


-0.021 


2311.115 


113,000 


758 


3564.582 


0.9 


0.07 


0.001 


3564.583 


3152,000 


760 


5123.042 


0.2 


-1.02 


-0.025 


5123 017 


202,000 


761 


3074.378 


0.7 


-0.89 


-0.013 


3074 . 365 


232,000 


762 


3672.189 


0.8 


-0.67 


-0.012 


3672.177 


307,000 



Number of lengths = 116 
Maximum length =29334.857 
Minimum length = 1049.944 
Average length = 9401.455 



STATISTICS 

Maximum positive v in seconds = 1 .64 
Maximum negative v in seconds = — 1 .83 
Average length v in seconds = 0.48 

Maximum positive v in meters = 0.088 



Maximum negative v in meters = —0.085 

Average length v in meters = 0.020 

The sum of pw in seconds = 38 . 882 

The sum of w in seconds = 46 . 972 






Horizontal Crustal Movements 



279 





Table 7C— Adjustment 2 adjusted positions of preearthqnake survey stations ' 


Station number 


Geographic position Plane coordinates — Zone VII 


Latitude Longitude X Y 



° ' " ° ' " Feet 

34 08 24.13977 118 38 41.07730 4092458.65 4163510.67 

34 07 43.28100 118 30 42.99104 4132637.67 4159283.96 

34 15 25.40288 118 38 22.91005 4094113.52 4206090.32 

34 20 14.88310 118 27 15.52367 4150169.04 4235236.47 

34 17 33.37539 118 24 19.55698 4164914.29 4218895.72 

34 17 21.86958 118 27 40.66687 4148038.58 4217749.14 

34 18 19.67125 118 25 58.17314 4156644.40 4223582.70 

34 19 30.09681 118 25 51.38379 4157220.78 4230701.46 

34 17 30.02684 118 29 14.32964 4140180.70 4218584.60 

34 15 27.78210 118 31 10.81270 4130384.47 4206243.31 

34 17 14.47217 118 32 23.72676 4124285.88 4217040.26 

34 18 42.15464 118 3158.45860 4126423.48 4225899.81 

34 19 12.75554 118 33 53.40644 4116787.92 4229013.60 

34 14 44.19154 118 29 16.78673 4139949.14 4201820.82 

34 15 48.73143 118 24 26.62495 4164313.57 4208317.78 

34 21 11.67515 118 24 58.73869 4161644.66 4240966.16 

34 08 13.09229 118 19 29.67663 4189241.55 4162250.29 

34 12 54.48125 118 16 44.67255 4203096.64 4190699.36 

34 09 48.84776 118 1145.00436 4228288.74 4171957.81 

34 13 25.51139 118 03 38.66758 4269098.71 4193941.79 

34 16 08.38754 118 14 17.09743 4215472.05 4210310.10 

34 20 55.42401 118 13 41.74959 4218408.90 4239329.46 

34 22 31.89283 118 10 28.65024 4234585.11 4249102.49 

34 22 54.69132 118 02 01.25847 4277109.61 4251502.69 

34 22 54.69132 118 02 01.25847 4277109.61 4251502.69 

34 30 06.10235 118 06 02.79330 4256765.54 4295062.44 

34 23 12.65759 118 1101.76462 4231803.32 4253219.27 

34 3150.26596 118 08 50.24493 4242730.91 4305564.10 

34 32 51.69884 118 12 52.65141 4222441.58 4311744.42 

34 27 35.29576 118 13 04.37755 4221496.83 4279756.66 

34 23 10.27166 118 19 02.69923 4191495.13 4252945.41 

34 23 10.87340 118 19 43.79002 4188051.18 4253005.90 

34 33 37.91377 118 21 18.24934 4180147.78 4316396.48 

34 33 39.50210 118 21 18.45957 4180130.23 4316557.06 

34 35 58.91390 118 23 49.57613 4167499.66 4330656.45 

34 34 01.29127 118 24 42.65010 4163053.45 4318768.25 

34 35 54.58823 118 27 08.84868 4150839.67 4330234.06 

34 33 24.32504 118 28 11.78987 4145557.29 4315049.54 

34 35 11.67296 118 3122.09963 4129659.17 4325927.45 

34 32 44.07320 118 29 56.70585 4136775.09 4310993.24 

34 32 00.69375 118 32 17.12304 4125019.70 4306629.09 

34 3102.85228 118 30 52.32750 4132103.90 4300768.19 

34 29 52.17562 118 33 00.98747 4121322.09 4293644.16 

34 29 29.17153 118 3103.91114 4131117.44 4291299.32 

34 28 45.12985 118 33 56.59444 4116652.23 4286876.49 

34 27 45.56377 118 32 23.74117 4124413.78 4280838.03 

34 27 50.61120 118 34 21.38566 4114563.78 4281369.80 

34 26 15.71204 118 32 31.67196 4123731.10 4271756.00 

34 25 46.76831 118 34 47.41080 4112354.32 4268855.36 

34 24 58.92063 118 32 21.39459 4124576.30 4263991.22 

34 23 38.46881 118 34 56.13483 4111591.88 4255887.09 

34 23 39.29371 118 32 04.87837 4125944.20 4255938.83 

34 2121.89486 118 35 24.07154 4109215.93 4242086.50 

34 20 39.21131 118 31 11.00518 4130425.79 4237725.55 

34 22 30.96394 118 32 06.97463 4125754.85 4249031.63 

34 2108.05995 118 25 43.10393 4157924.49 4240603.94 

34 19 47.21373 118 36 00.20706 4106161.23 4232522.93 

34 19 49.65440 118 36 00.57705 4106130.85 4232769.74 

34 3157.06378 118 28 39.91802 4143192.06 4306231.04 

34 29 46.73378 118 40 03.80617 4085929.47 4293189.59 

61 34 34 02.76707 118 44 30.62758 4063699.20 4319154.45 

62 34 34 03.16369 118 44 30.86546 4063679.46 4319194.62 

63 34 35 43.94430 118 34 43.89337 4112794.17 4329225.93 

64 34 4135.34144 118 33 37.71564 4118406.03 4364738.89 

1 The geographic position of station Cahuenga 2, No. 17, is adjusted to North American Datum of 1927. All other stations depend on 
this position. 



280 San Fernando Earthquake of 1971 



Table 7I>.—Atijitstinrnt 2 adfutUd pOritiom Of poslfarthf/uakf survey \latitms > 



Orographic position Plan'- < oordinat<-s, Zone VII 
Station number 

Latitude Longitude X Y 

° ' ~ • ' "~ 

701 34 OH 24 11077 118 38 4107730 4092456 4163510.67 

702 34 07 43.64153 1 18 30 43.02482 4132634 89 4159320 41 

703 34 1.5 25.40288 I 18 38 22 91005 40041 I '. 02 4206090 

704 34 20 14.87888 118 27 10 53168 4150168 37 4230236 05 

705 34 17 33.38836 118 24 19.63485 4164007 70 4218807 04 

706 34 17 22 2028 r . 118 27 40.15361 414808170 421770187 

707 34 18 19.67348 1 18 20 58 21 (04 41 06641 60 422308/ 

709 34 17 30 02589 118 20 14 33027 4140179 90 4218084 01 

710 34 15 27.78853 1 18 31 10.80821 4130384 80 420624 - 

711 34 17 14.47568 118 32 23 72606 4124280 90 4217040 62 

712 34 18 42.15481 118 3108.46001 4126423.32 4225899.83 

713 34 19 12.81727 118 33 5138439 4116907 04 4220010 40 

715 34 15 48.74701 118 24 26 61700 4164314 23 4206319.36 

717 34 08 13.09229 118 19 29 67' 4189241.55 4162200 29 

718 34 12 52.92497 118 16 40 1,8322 4202670 01 419054182 

719 34 09 48.84776 118 1145.00430 4228288.74 4171957.81 

720 34 13 21.28581 1 18 03 42 .05 ! 1 4268815.55 4193013.88 

721 34 16 08.38780 118 14 17.09324 4215472.40 4210310. 13 

724 34 22 54.69132 118 02 01.25847 4277109 61 4251502.1 

726 34 27 35.11464 118 13 04.13472 4221517.18 4279738.37 

727 34 23 12.65693 118 1101.76913 4231802.94 4253219.20 

729 34 32 51.69884 118 12 52.65141 4222441.58 4311744.42 

730 34 27 35.29287 118 13 04.37698 4221496.87 4279756.37 

731 34 23 10.26555 118 19 02.69767 4191495 26 4252944.79 

732 34 23 10.86696 118 19 43.79093 4188051.11 4253005.25 

733 34 33 37.91377 118 2118.24934 4180147.78 43163%. 48 

734 34 33 39.50210 118 2118.45957 4180130.23 4316557.06 

735 34 20 39.20843 118 3111.00754 4130425.59 4237725.26 

736 34 19 46.09173 118 35 59.05454 4106257.60 4232409.25 

737 34 19 49.65440 118 36 00.57705 4106130.85 4232769.74 

738 34 2108.04736 118 25 43.11244 4157923.78 4240602.67 

739 34 22 30.96343 118 32 06.97687 4125754.67 4249031.58 

740 34 2121.89508 118 35 24.07181 4109215.91 4242086.52 

741 34 23 39.29311 118 32 04.88166 4125943.92 4255938.77 

742 34 23 38.46908 118 34 56.13641 4111591.75 4255887.12 

743 34 24 58.91927 118 32 21.39657 4124576.13 4263991.09 

744 34 25 46.76846 118 34 47.41248 4112354.18 4268855.38 

745 34 26 19.78917 118 32 29.50542 4123913.42 4272167.80 

746 34 27 50.61004 118 34 21.38730 4114563.64 4281369.68 

747 34 27 45.56395 118 32 23.74168 4124413.74 4280838.04 

748 34 28 45.13028 118 33 56.59556 4116652. 14 4286876.53 

749 34 29 29.17241 118 3103.91204 4131117.36 4291299.41 

750 34 29 52.17640 118 33 00.98801 4121322.04 4293644.24 

751 34 3102.85293 118 30 52.32848 4132103.82 4300768.26 

752 34 3157.06461 118 28.39.91467 4143192.34 4306231.12 

753 34 33 24.32628 118 28 11.78994 4145557.28 4315049.66 

754 34 32 44.07415 118 29 56.70713 4136774.99 4310993.34 

755 34 35 11.67296 118 3122.09963 4129659.17 4325927.45 

756 34 32 00.69415 118 32 17.12349 4125019.66 4306629.13 

757 34 3101.29173 118 34 57.80275 4111561.46 4300653.75 

758 34 32 35.80760 118 33 37.20989 4118326.97 4310193.11 

759 34 33 46.16086 118 32 48.70735 4122399.44 4317296.77 

760 34 30 06.68395 118 38 07.49398 4095671.18 4295176.09 

761 34 3120.20981 118 36 56.15251 4101662.87 4302592.06 

762 34 32 37.32392 118 36 01.21403 4106280.40 4310375.55 

763 34 34 40.92218 118 34 51.89368 4112109.84 4322856.22 

764 34 29 46.73378 118 40 03.80617 4085929.47 4293189.59 

765 34 34 03.16369 118 44 30.86546 4063679.46 4319194.62 

766 34 34 02.76707 118 44 30.62758 4063699.20 4319154.45 

767 34 35 43.94430 118 34 43.89337 4112794.17 4329225.93 

768 34 4135.34144 118 33 37.71564 4118406.03 4364738.89 

1 The geographic position of station Cahuenga 2, No. 717, is adjusted to North American Datum of 1927. All other stations depend on this 
position. 



Horizontal Crustal Movements 281 



Table 8B.— Adjustment 2 position shijts referred to station Cahuenga 2 



Station 



Postearthquake minus preearthquake 



Resultant vector 



Bluff 

Brushy 

Bum 

Cahuenga 2 

Calabasas 

Chatsworth 

Corner 2 

Deer 

Dry 

East 

Edison 

Flint 

Hauser 

House 

Lock 

Loma Verde 

Long 

Magic 

May 

Mission Pt 

Mt. Gleason 

Newhall 

Pacifico 

Pacoima E-2 ECC 1 

Pacoima L-l 

Pacoima No. 2 

Parker 

Pelona 

Pelona ECC 2 

Pico L-9 AUX 2 ECC 1 

Port 

Powerhouse 

Red 

Reservoir 

Rock 

Saugus 

Sawmill 

Sister Elsie 

Steer 

Sylmar F-8 

Sylmar 1-12 

Towsley 

Verdugo AUX 

View 

Warm Springs 

Whitaker 

WPK A-7A AUX 1 

Yucca 



AX 


AT 


L 


Azimuth 


Feet 


Feet 


Feet 


o 


+0.02 


+0.36 


0.36 


180 


-0.10 


+0.10 


0.14 


135 


-0.09 


+0.04 


0.10 


115 



































+0.38 


+0.65 


0.75 


2J0 


+0.28 


+0.08 


0.29 


255 


-0.04 


+0.01 


0.04 


105 


-0.20 


-0.29 


0.35 


35 


-0.18 


-0.05 


0.19 


75 
























-0.01 


+0.12 


0.12 


175 


-0.13 


+0.03 


0.13 


105 













-0.14 


-0.12 


0.18 


50 


+0.13 


-0.62 


0.63 


350 


-0.71 


-1.27 


1.45 


30 


-0.16 


+0.02 


0.16 


95 


-0.38 


-0.07 


0.39 


80 


-0.28 


-0.06 


0.29 


80 













+0.40 


-0.54 


0.67 


325 


-6.54 


+ 1.32 


6.67 


100 


+0.66 


+ 1.58 


1.71 


205 


+0.04 


-0.29 


0.29 


350 



































-0.07 


-0.65 


0.65 


5 


-0.04 


+0.04 


0.06 


135 













-0.80 


-0.09 


0.80 


85 


-0.08 


+0.07 


0.11 


130 


-0.17 


-0.13 


0.21 


55 













+0.35 


+0.03 


0.35 


265 


-0.05 


+0.08 


0.09 


150 


-0.67 


-0.42 


0.79 


60 


-3.35 


+0.23 


3.36 


95 


-0.02 


+0.02 


0.03 


135 


+0.21 


-0.06 


0.22 


285 


-0.08 


+0.09 


0.12 


140 



































-0.14 


+0.02 


0.14 


ioo 



282 San Fernando Earthquake of 1971 



APPARENT HORIZONTAL DISPLACEMENT 








Scale for Vectors and Ellipses 










1 2 3 4 5 6 7 Feet 






768 . 




1 2 Meters 









5 Miles b 


10 


Km 


767i 

755- 






765 *766 

•754 
756 „ 752 


^734 
733 

'-729 






'751 








764 a 750- >?49 








748 c 








746 » °747 


% 730 






744 » 








*743 Epicen 


ter 






742 • W41 ® 
-739 


732* ^731 - 727 




724 


740 o 738 
735 f 
7,7 r 704 / 
737 ^736 ' f 








709"" — ~——705 
711* —* *706^^, 

* / 
/ San Fernando </ 

703. 7 / 715 


721 - 








718 » 




a 720 


A 

701 a 


717 7l9 
CAHUENGA 2 






702 


( Held Fixed ) 







Figure 2B. — Adjustment 2 position vectors referred to station Cahuenga 2. 



Horizontal Crustal Movements 



283 



Table 5E.— Adjustment 3 corrections to preearthquake observed horizontal directions 





Station 






Station 






Station 






Station 




From 


To 


V 


From 


To 


V 


From 


To 


V 


From 


To 




1 






13 






21 






33 








2 


-0.73 




11 


0.56 




23 


0.49 




59 


0.52 




3 


0.04 




12 


-0.57 




31 


0.09 


34 








14 


0.61 




54 


-0.18 




56 


0.67 




26 


-0.64 




57 


0.09 




57 


0.21 


22 








30 


-0.24 


2 






14 








21 


0.31 




31 


-1.39 




1 


0.71 




1 


-0.31 




23 


0.57 




35 


0.59 




3 


0.20 




2 


0.31 




31 


-0.88 




36 


0.49 




14 


1.00 




3 


-0.84 


23 








39 


0.27 




15 


-0.12 




5 


0.22 




20 


-0.27 




56 


0.45 




16 


-0.10 




6 


0.42 




21 


-0.32 




60 


0.05 




17 


-1.09 




15 


0.04 




22 


-0.81 




64 


0.41 




18 


-0.01 




16 


0.93 




24 


0.65 


35 








57 


-0.58 




17 


-0.93 




26 


0.64 




34 


-1.08 


3 








57 


0.17 




30 


0.04 




36 


-0.27 




1 


0.40 


15 








31 


0.06 




37 


0.21 




2 


-0.26 




2 


0.09 


24 








38 


1.22 




14 


0.52 




4 


0.03 




20 


-0.57 




39 


0.34 




16 


-0.58 




5 


-0.10 




23 


-0.73 




64 


-0.41 




57 


-0.07 




6 


-0.11 




26 


1.30 


36 






4 








9 


0.92 


25 








34 


0.05 




5 


-0.10 




14 


-0.41 




27 


-0.78 




35 


-0.06 




6 


0.01 




16 


-0.90 




28 


0.27 




37 


0.49 




7 


0.30 




17 


-0.07 




29 


0.52 




38 


-0.47 




8 


-0.13 




18 


0.08 


26 






37 








15 


-0.10 




21 


0.82 




23 


-0.74 




35 


-0.69 


5 








56 


-0.15 




24 


-0.99 




36 


0.18 




4 


0.24 




57 


-0.20 




30 


0.44 




38 


0.14 




6 


0.06 


16 








34 


1.29 




39 


0.45 




7 


-0.20 




2 


-0.20 


27 








40 


-0.06 




8 


0.02 




3 


-0.04 




25 


-0.01 


38 








14 


-0.23 




6 


0.12 




28 


0.34 




35 


0.10 




15 


0.10 




9 


1.11 




29 


-0.22 




36 


0.33 


6 








14 


-0.10 




30 


0.60 




37 


-0.47 




4 


0.36 




15 


-0.79 




32 


-0.41 




39 


0.02 




5 


0.07 




17 


-0.36 




33 


-0.30 




40 


0.03 


» 


7 


-0.34 




18 


-0.61 


28 






39 








8 


-0.28 




21 


0.41 




27 


0.04 




34 


-0.89 




9 


0.33 




56 


0.20 




29 


-0.14 




35 


-0.15 




14 


-0.03 




57 


0.22 




30 


0.11 




37 


-0.14 




15 


0.11 


17 






29 








38 


0.06 




16 


-0.11 




2 


0.83 




25 


-1.08 




40 


0.84 




56 


-0.11 




14 


0.08 




27 


-1.07 




41 


0.16 


7 








15 


-0.09 




28 


0.32 




42 


-0.65 




4 


-0.84 




16 


-0.43 




30 


0.85 




56 


-0.69 




5 


0.02 




18 


-0.35 




32 


0.31 




60 


0.20 




6 


0.43 




19 


0.44 




33 


0.68 




63 


1 .18 




8 


0.40 




20 


-0.08 


30 








64 


0.08 


8 








21 


-0.41 




23 


-0.07 


40 








4 
5 


0.28 
0.09 


18 


2 


-0.68 




26 

27 


-0.63 
0.02 


37 
38 
39 
41 
42 


-0.27 

0.21 

-0.13 

-0.02 

0.20 


9 


6 

7 


-0.22 
-0.16 




15 
16 
17 


-0.08 

-0.05 

0.59 




28 
29 

31 


-0.46 

0.53 

-0.26 






6 


-0.32 




19 


-0.48 




32 


0.56 








10 


-0.42 




20 


0.77 




33 


0.22 


41 


39 
40 
42 
43 
44 


-0.31 
-0.36 

0.39 
-0.28 

0.53 




11 


0.53 




21 


-0.01 




34 


0.10 






12 


0.17 




56 


-0.06 


31 










15 


0.38 


19 








21 


-0.42 






16 


0.34 




17 


1.15 




22 


0.54 






56 


-0.68 




18 


-0.26 




23 


0.24 




10 








20 


-0.67 




30 


0.49 


42 








9 


0.01 




21 


-0.23 




32 


-1.54 




39 


-0.02 




11 


-0.68 


20 








34 


-0.98 




40 


0.36 


11 


12 


0.65 




17 
18 


0.04 
-0.15 


32 


56 


1.69 




41 
43 


-0.10 
-0.27 




9 


0.14 




19 


0.43 




27 


-0.25 




44 


0.01 




10 


-0.09 




21 


-0.64 




29 


-0.07 


43 








12 


-0.50 




23 


0.33 




30 


-0.42 




41 


-0.09 




13 


0.93 




24 


0.48 




31 


1.51 




42 


0.18 




56 


0.87 




57 


-0.49 




33 


0.27 




44 


0.02 




57 


-1.34 


21 








56 


-1.09 




45 


-0.28 


12 








15 


-0.16 




59 


0.09 




46 


0.17 




9 


0.11 




16 


-0.84 


33 






44 








10 


0.83 




17 


-0.53 




27 


-0.36 




41 


-0.73 




11 


-0.59 




18 


-0.09 




29 


-0.85 




42 


0.43 




13 


0.86 




19 


0.44 




30 


-0.77 




43 


-0.32 




54 


-0.25 




20 


0.57 




32 


0.76 




45 


0.62 




56 


-0.95 




22 


-0.64 




56 


0.70 




46 


-0.03 



281 



San Fernando Earthquake <>f 1971 



Table SB.— Adjustment J corrections i<> preearthquake observed horizontal directions— ContltmeA 



Station 



Station 



Station 






From 



To 



I IOIII 



To 



From 



To 






To 



45 



46 



47 



48 



49 



50 



51 



43 
44 
46 
47 
48 

43 
44 
45 
47 
48 

45 
46 
48 
49 
50 

45 
46 
47 
49 
50 

47 
48 
50 
51 
52 
56 

47 
48 
49 
51 
52 

49 



-0.20 
-0.30 

0.06 
-0.17 

0.60 

0.18 

. 34 
-0.31 
-0.22 

0.01 

-0.17 

0.49 

-0.18 

-0.59 

0.47 

-0.14 

0.29 

-0.10 

-0.21 

0.16 

0.04 
0.34 
■0.34 
-0.39 
-0.69 
0.64 

-0.36 
0.14 
0.15 

-0.09 
0.14 

-0.50 



51 



52 



56 



53 



54 



55 



56 



r ,o 
52 
53 
55 

49 
50 
51 
53 
54 
55 
56 
57 

51 
52 
54 
55 

57 

12 
13 
52 
53 
55 
56 
57 

51 
52 
53 
54 

57 

6 

9 

11 

12 

15 



0.27 

-0 10 

-I) 01 
0. 13 

61 

o 13 

30 

-0.05 

-0.08 

o 35 

-0 71 

-0.56 

-0.24 
-0.53 

0.20 
-0.34 

-0.14 
1.59 
-0.12 
-0.73 
-0.47 
0.66 
-0.78 

-0.81 
0.01 

-0.12 
0.65 
0.26 

0.62 
-0.73 

0.17 
-0.04 

1.28 



57 



58 



16 
18 

21 
31 
J2 
53 

34 
39 

54 
57 
58 
59 
60 
61 
64 



56 
59 
61 
63 



-0 40 
01 

-o 09 
27 

-0 44 
25 
Tl 

-0 96 
0.84 

71 
0.12 

-1.73 
-0.24 
-0 60 

1 29 
-0 39 



1 


-1 .28 


2 


-1 19 


3 


0.71 


11 


-0.27 


13 


1.56 


14 


-0 04 


15 


-1.22 


16 


-0.63 


20 


-0.21 


52 


0.71 


53 


-0.07 


54 


0.02 


55 


0.69 


56 


0.01 


59 


0.99 


60 


-0.71 


62 


1.52 



-0.31 
0.00 
0.26 
0.05 






60 



61 



62 



63 



64 



32 
61 

39 

62 

64 

33 

56 

59 

34 

57 

60 
63 



34 
35 
39 
56 
60 
63 



-0 12 

10 

-0 34 
64 

-1.07 

74 

1 05 

0.33 
0.05 
0.30 

-0.66 
1 00 

0.33 

-0.79 

0.11 



39 


0.36 


58 


-1.45 


59 


-1.18 


60 


1 25 


02 


-0.39 


04 


1.41 



0.10 
-1.19 

0.29 
-0.64 

0.49 

0.95 



Horizontal Crustal Movements 



285 



Table 5F.— Adjustment 3 corrections to postearthquake observed horizontal directions 





Station 


„ 




Station 






Station 






Station 




From 


To 




From 


To 


V 


From 


To 


V 


From 


To 




701 






719 






735 






746 








702 


0.15 




717 


-0.91 




737 


-0.22 




747 


-0.07 




703 


0.41 




718 


-0.21 




738 


-0.56 




748 


0.28 




706 


-0.56 




720 


0.44 




739 


-0.15 




752 


0.52 


702 








721 


0.67 




740 


-0.35 




757 


0.14 




701 


0.25 


720 








741 


0.17 




764 


0.20 




703 


0.27 




719 


-0.51 


736 








766 


-1.30 




706 


-0.68 




721 


0.31 




703 


-0.86 


747 








715 


-0.60 




724 


0.20 




710 


1.12 




745 


-0.85 




717 


0.76 


721 








713 


1.13 




746 


-0.61 


703 








715 


-1.86 




717 


-0.63 




748 


-0.05 




701 


0.86 




717 


-0.45 




735 


0.42 




749 


1.83 




702 


-0.36 




719 


0.43 




738 


-1.17 




750 


0.07 




706 


-0.25 




720 


-0.16 


737 








752 


-0.74 




736 


0.25 




724 


0.50 




713 


0.71 




766 


0.34 




738 


-0.50 




727 


-0.62 




735 


-0.06 


748 






704 








731 


0.91 




738 


-0.44 




745 


0.02 




705 


0.05 




732 


1.05 




739 


0.87 




746 


0.00 




706 


0.11 




738 


0.20 




740 


-0.60 




747 


0.16 




709 


-0.07 


724 








752 


-0.31 




749 


-0.50 




738 


-0.09 




720 


-0.03 




764 


0.29 




750 


0.07 


705 








721 


0.40 




765 


-0.24 




757 


0.30 




704 


0.34 




726 


-0.62 




766 


-0.25 




764 


-0.08 




706 


0.06 




727 


-0.05 


738 






749 








709 


0.25 




729 


0.30 




703 


0.69 




747 


-0.69 




738 


-0.63 


726 








704 


-0.04 




748 


0.45 


706 








724 


0.22 




705 


0.09 




750 


-0.06 




701 


0.95 




727 


0.40 




706 


-0.51 




751 


0.58 




702 


0.84 




729 


-0.28 




709 


-0.41 




756 


-0.30 




703 


1.51 




732 


-0.35 




710 


-0.52 


750 








704 


-0.46 


727 








712 


1.25 




747 


0.06 




705 


-1.11 




721 


0.32 




715 


0.68 




748 


-0.05 




709 


-0.96 




724 


1.36 




721 


-0.01 




749 


-0.43 




715 


-0.57 




726 


-0.55 




732 


0.01 




751 


-0.41 




717 


0.70 




732 


-1.13 




733 


-0.72 




752 


0.39 




738 


-0.88 


729 








734 


-2.04 




754 


0.27 


709 








724 


-1.01 




735 


0.63 




756 


0.13 




704 


0.49 




726 


0.08 




736 


0.62 




757 


0.04 




705 


0.58 




730 


0.08 




737 


-0.06 


751 








706 


0.00 




732 


1.11 




741 


1.20 




749 


0.04 




711 


-1.51 




734 


-0.27 




752 


0.02 




750 


-0.28 




712 


0.04 


730 








764 


-0.90 




754 


-0.30 




738 


0.41 




729 


-0.31 




766 


0.01 




755 


0.44 


711 








732 


-0.17 


739 








756 


0.09 




709 


0.38 




733 


0.25 




735 


0.17 


752 








710 


0.51 




734 


0.23 




737 


-0.89 




732 


-0.16 




712 


-0.02 


731 








740 


-0.08 




734 


-0.57 




713 


-0.88 




732 


0.24 




741 


0.26 




737 


0.56 


712 








734 


-0.27 




742 


0.53 




738 


0.51 




709 


-0.17 


732 






741 








746 


-0.33 




710 


-0.92 




721 


1.12 




735 


0.54 




747 


-0.21 




711 


0.74 




726 


-0.17 




738 


-0.78 




750 


1.02 




713 


-0.16 




727 


0.40 




739 


-0.52 




753 


0.56 




735 


0.24 




729 


0.47 




740 


-0.29 




754 


-0.08 




738 


0.28 




730 


-0.17 




742 


0.53 




755 


1.23 


713 








731 


-0.32 




743 


0.48 




756 


— 1.31 




711 


1.43 




733 


-1.55 




744 


0.06 




764 


-1.38 




712 


-0.13 




734 


-1.36 


743 








765 


-0.84 




735 


0.46 




738 


0.89 




741 


-0.65 




766 


1.98 




736 


0.07 




752 


0.68 




742 


-0.06 




767 


-0.97 




737 


-1.82 


733 








744 


-0.44 


753 






715 








729 


-0.93 




745 


0.39 




752 


-0.19 




702 


-0.44 




730 


-0.14 




746 


0.78 




754 


-0.32 




706 


-0.66 




732 


0.33 


744 








755 


0.51 




717 


0.70 




738 


0.74 




741 


-0.66 


754 








721 


0.03 


734 








742 


0.41 




750 


0.11 




738 


0.36 




729 


0.46 




743 


-0.41 




751 


0.30 


717 








730 


0.47 




745 


0.29 




752 


0.17 




702 


0.66 




731 


1.42 




746 


0.36 




753 


-0.09 




706 


0.29 




732 


-0.34 


745 








755 


0.30 




715 


-0.58 




738 


-0.37 




743 


-0.71 




756 


-0.58 




718 


0.28 




752 


-0.17 




744 


0.46 




759 


-0.21 




719 


-1.04 




755 


0.44 




746 


0.00 


755 








721 


0.43 




765 


-1.11 




747 


0.61 




734 


-0.43 




736 


-0.03 




768 


-0.78 




748 


-0.36 




751 


-0.22 


718 






735 






746 








752 


0.34 




717 


0.22 




712 


0.37 




743 


1.05 




753 


0.14 




719 


-0.53 




713 


-0.08 




744 


-0.72 




754 


0.43 




721 


0.31 




736 


0.83 




745 


-0.11 




756 


-0.15 



286 



San Fernando Earthquake <>\ 1971 



Table 5F.— Adjustment > corrections to potUarthquake oburved botixonUd direction* < nnnntu-d 





Station 






Station 


.," 


Station 


„* 








From 


To 




From 


To 




From i o 






To 




755 






t;,: 






762 




765 








759 


0.04 




756 


0.15 




0.40 






34 




764 


-0.26 




757 


-1 .02 




-0 19 




764 


57 




767 


0.37 




759 


0.00 


761 


0.00 




767 


-0.32 




768 


-0.28 




762 


-0 12 


76 5 


-0 04 


766 






756 








763 


1 .01 


763 






737 


1 42 




749 


0.62 


759 






758 


-0 65 






-0 24 




750 


-0.05 




754 


-0.67 


7 59 


-0 72 




746 


-1 82 




751 


0.35 




7 55 


20 


762 


79 




747 


0.80 




752 


0.45 




756 


0.11 


7b7 


59 




752 


-0.17 




754 


0.50 




7 58 


-0.06 


764 




767 








755 


-1 .88 




762 


0.09 


737 


5'* 




7 52 


43 




757 


-0.36 




71,3 


0.77 


1 18 


1 02 




755 


01 




758 


0.17 




767 


-0.43 


746 


-0 02 




757 






759 


0.17 


760 






748 


0.18 






-0.14 


757 








757 


-0.11 


752 


15 




760 


-0 13 




746 


0.02 




761 


0.04 


755 


0.03 




761 


-1.08 




748 


-1 .01 




767 


0.07 


7 57 


<)') 






-0 15 




750 


-0.17 


761 






761 


-2.22 




764 


0.83 




756 


-0.32 




757 


-0.93 


765 


0.18 




765 


0.40 




758 


0.29 




71.0 


M 02 


767 


80 




768 


32 




760 


0.04 




762 




768 


-1 .00 


768 








761 


0.29 




764 


0.70 


765 






734 


14 




762 


-0.22 




767 


-0.10 


734 


0.21 




755 


0.11 




764 


-0.31 


762 






737 


-1.33 




764 


0.34 




767 


1.41 




757 


-0.14 


738 






767 


-0.57 



Table 6E.— Adjustment 3 corrections to preearthquake observed lengths (v's) in meters 





Station 




Observed 


Weight 


v in 


v in 


Adjusted 










length 


factor 


seconds 


meters 


length 


1 part in 








From 




To 














1 




3 
17 
56 


12988.206 

29502.131 

1139.270 


1.0 
1.0 
0.3 


0.27 
1.24 
1.39 


0.017 

0.177 
0.008 


12988.223 

29502 . 308 

1139.278 


762,000 
166,000 
148,000 


1 




16 




31 




32 


1049.944 


0.1 


- 1 3 . 39 


-0.068 


1049.876 


15,000 


31 




34 


19695.796 


2.4 


-0.18 


-0.017 


19695.779 


1134,000 


34 




64 


23866.161 


2.4 


0.58 


0.068 


23866.229 


353,000 


39 




63 


5237.752 


0.6 


0.18 


0.004 


5237.756 


1170,000 


60 




63 


13700.048 


1.6 


-0.56 


-0.037 


13700.011 


370,000 



Number of lengths = 8 

Maximum length =29502.131 
Minimum length = 1049.944 
Average length =13397.413 



STATISTICS 

Maximum positive v in seconds = 1 . 39 
Maximum negative v in seconds = — 13.39 
Average length v in seconds = 2.22 

Maximum positive v in meters = 0. 177 






Maximum negative v in meters = —0.068 
Average length v in meters = 0.050 

The sum of pvv in seconds = 6.537' 

The sum of vv in seconds = 183.675 



Horizontal Crustal Movements 



287 



Table 6F.— Adjustment 3 corrections to postearthquake observed lengths (v's) in meters 



Station 



From 



To 



Observed 
length 



Weight 
factor 



v in 
seconds 



v in 
meters 



Adjusted 
length 



1 part in 



701 702 

701 703 

701 706 

702 703 

702 706 

702 715 

702 717 

703 736 

704 705 

704 706 

704 707 

704 709 

704 738 

705 706 

705 709 

705 738 

706 707 

706 709 

706 715 

706 738 

709 711 

709 712 

709 738 

710 711 

710 712 

710 736 

710 738 

711 712 

711 713 

712 713 

712 735 

712 738 

713 735 

713 737 

715 738 

717 718 

718 721 

719 720 

720 724 

721 727 

721 732 

721 738 

724 730 

727 730 

727 732 

729 730 

729 732 

729 734 

730 732 

730 734 

731 732 

731 734 

732 734 

732 738 

732 752 

733 738 

734 738 

734 752 

734 755 

734 768 

735 737 

735 738 

735 739 

735 740 

735 741 

736 738 

737 738 

737 739 

737 740 

737 752 

737 766 

738 741 

738 752 

738 764 

739 740 

739 741 

739 742 

740 741 

740 742 



12312.320 


1.0 


-0.66 


-0.039 


12312.281 


12988.248 


1.0 


0.15 


0.010 


12988.258 


23689.237 


1 .0 


0.24 


0.027 


23689.264 


18468.538 


1.0 


-0.10 


-0.009 


18468.529 


18433.678 


1.0 


0.58 


0.051 


18433.729 


17784.643 


1.0 


0.08 


0.007 


17784.650 


17277.090 


1.0 


-0.54 


-0.045 


17277.045 


8834.865 


1.0 


0.56 


0.024 


8834 . 889 


6707.119 


1.2 


0.39 


0.013 


6707.132 


5354.937 


0.8 


-0.06 


-0.001 


5354.936 


4063.040 


0.6 


-0.00 


-0.000 


4063.040 


5918.553 


0.8 


-0.48 


-0.014 


5918.539 


2874.647 


0.4 


-0.45 


-0.006 


2874.641 


5139.684 


0.8 


-0.13 


-0.003 


5139.681 


7537.743 


1.2 


-0.35 


-0.013 


7537.730 


6949.956 


0.7 


0.30 


0.010 


6949 . 966 


3149.940 


0.8 


0.01 


0.000 


3149.940 


2420.603 


0.7 


-1 .45 


-0.017 


2420 . 586 


5728.547 


1 .0 


0.10 


0.003 


5728.550 


7572.380 


0.7 


-0.64 


-0.024 


7572.356 


4867.378 


0.9 


-1.36 


-0.032 


4867 . 346 


4749.053 


0.6 


-0.58 


-0.013 


4749.040 


8619.200 


0.7 


0.11 


0.005 


8619.205 


3779.620 


0.7 


-0.00 


-0.000 


3779.620 


6111.645 


0.7 


-0.16 


-0.005 


6111.640 


10848.427 


0.8 


-1 .04 


-0.055 


10848.372 


13421 .494 


1.0 


-1.20 


-0.078 


13421 .416 


2777.813 


0.5 


-1.36 


-0.018 


2777.795 


4280.273 


0.5 


-0.56 


-0.012 


4280.261 


3037.845 


0.6 


0.29 


0.004 


3037.849 


3805.260 


0.7 


0.04 


0.001 


3805.261 


10595.807 


1 .1 


-0.29 


-0.015 


10595.792 


4888.063 


0.7 


-0.06 


-0.001 


4888.062 


3492 . 387 


0.7 


-0.20 


-0.003 


3492.384 


10030.937 


1.0 


0.77 


0.037 


10030.974 


9546 . 200 


l.l 


0.28 


0.013 


9546.213 


7177.706 


0.8 


-0.39 


-0.014 


7177.692 


13991 .396 


0.9 


0.31 


0.021 


13991 .417 


17855.019 


1.4 


0.05 


0.004 


17855.023 


13993.997 


1.3 


-0.52 


-0.035 


13993.962 


15466.399 


1.6 


0.46 


0.035 


15466.434 


19822.690 


1 .5 


0.15 


0.014 


19822.704 


19012.978 


1.2 


-0.64 


-0.059 


19012.919 


8677.040 


0.8 


1.52 


0.064 


8677.104 


13335.795 


1.0 


-0.23 


-0.015 


13335.780 


9754.135 


1 .1 


0.20 


0.009 


9754.144 


20746.517 


1.8 


-0.24 


-0.024 


20746.493 


12979.516 


1.5 


-0.36 


-0.023 


12979.493 


13054.013 


1.4 


-0.01 


-0.001 


13054.012 


16875.648 


1.5 


0.55 


0.045 


16875.693 


1049.944 


0.4 


-0.01 


-0.000 


1049.944 


19695.934 


1.8 


0.25 


0.024 


19695.958 


19520.397 


1.8 


-0.06 


-0.005 


19520.392 


9930.636 


1.2 


-1 .48 


-0.071 


9930.565 


21216.619 


1.5 


-0.86 


-0.088 


21216.531 


24074.486 


1.7 


0.45 


0.052 


24074.538 


24119.961 


1.7 


0.39 


0.045 


24120.006 


11690.213 


1.2 


-0.52 


-0.030 


llh90.183 


15646.220 


1 .5 


0.13 


0.010 


15646.230 


23866.176 


1.8 


0.46 


0.053 


23866.229 


7557 . 594 


0.9 


-0.31 


-0.012 


7557.582 


8427.302 


0.9 


-0.71 


-0.029 


8427.273 


3728.717 


0.6 


-1.42 


-0.026 


3728.691 


6600.029 


1.0 


-0.38 


-0.012 


6600.017 


5717.114 


0.9 


-0.50 


-0.014 


5717.100 


15944.742 


1.7 


0.45 


0.035 


15944.777 


15966.080 


1.7 


0.71 


0.055 


15966.135 


7768.221 


0.8 


0.15 


0.006 


7768.227 


2991 .420 


0.6 


-0.25 


-0.004 


2991.416 


25079.104 


1.9 


0.79 


0.096 


25079 . 200 


29334.857 


1.0 


0.10 


0.014 


29334.871 


10810.436 


0.9 


-0.80 


-0.042 


10810.394 


20501.246 


1.8 


0.36 


0.036 


20501 .282 


27174.347 


1.6 


0.20 


0.026 


27174.373 


5467.488 


0.7 


-0.45 


-0.012 


5467.476 


2106.121 


0.6 


-0.98 


-0.010 


2106.111 


4796.027 


1 .0 


-0.56 


-0.013 


4796.014 


6620.000 


0.8 


-1.10 


-0.035 


6619.965 


4268.324 


0.6 


0.06 


0.001 


4268 . 325 



312 


,000 


1366 


,000 


864 


,000 


2000 


,000 


358 


,000 


2548 


,000 


382 


,000 


368 


,000 


536 


,000 


3617 


,000 







430 


,000 


462 


,000 


1618 


,000 


596 


,000 


694 


000 


22251 


000 


142 


000 


2040 


000 


322 


000 


152 


000 


353 


000 


1876 


000 


61572 


000 


1305 


000 


198 


000 


172 


000 


152 


000 


366 


000 


709 


000 


4747 


000 


714 


000 


3531 


000 


1034 


000 


269 


000 


743 


000 


527 


000 


676 


000 


4040 


000 


396 


000 


447 


000 


1406 


000 


325 


000 


136 


000 


905 


000 


1053 


000 


865 


000 


568 


000 


20422 


000 


377 


000 


16648 


000 


817 


000 


3637 


000 


140 


000 


241 


000 


459 


000 


533 


000 


396 


000 


1636 


000 


453 


000 


657 


000 


290 


000 


145 


000 


548 


000 


417 


000 


456 


000 


292 


000 


1362 


000 


831 


000 


260 


000 


2119 


000 


257 


000 


571 


000 


1047 


000 


455 


000 


211, 


000 


366, 


000 


187, 


000 


3199, 


000 



288 



San Fernando Earthquake of 1971 



Table 6F.— Adjustment J correction* to pOiUarthquakt observed lengths- (v'ij in nwters—f.ontinued 





Si.,1 


ion 


Observed 


Weight 


v in 


v in 


Adju 










length 


l.i' I'n 


<nds 


meb 


length 


1 part in 








From 




To 














741 




742 


4374.583 


<> 


16 


003 


4 574 


1517, 000 


741 




743 


2489.515 


0.7 


-0 63 


-0 008 


2489 507 




000 


741 




744 


5714.684 


1.2 


-0.73 


-0.020 


5714 664 


281 


000 


742 




743 


4665.227 


9 


15 


003 


4665 230 


1374 


000 


742 




744 


3959 . 540 


0.8 


(i 'c, 


018 


J959 558 


221 


000 


743 




744 


4009.449 


1 


u i-, 


008 


4009 457 


485 


000 


743 




745 


2500.442 


0.6 


-0.59 


-0.007 


2500 


349 


000 


743 




746 


6113 238 


1 1 


-0 01 


-0.001 


6113 217 


4884 


000 


744 




745 


3665.062 


0.8 


0.17 


oo I 


J665 065 


1196 


000 


744 




746 


3873.355 


0.8 


-0.24 


- 004 


J873 351 


868 


000 


745 




746 


3998.506 


0.9 


-0.79 


-0.015 


',998 491 


26 3 


000 


745 




747 


2647.091 


0.7 


-0.43 


-0.006 


2647 085 


481 


000 


745 




748 


4999 .769 


9 


-0.39 


-0.009 


4999 760 


527 


000 


746 




747 


3006 661 


0.8 


0.88 


0.013 


3006.674 


•/'A 


000 


746 




748 


1795. 146 


5 


-0.83 


-0.007 


1795.139 


249 


000 


746 




752 


11557.006 


1 .0 


12 


0.007 


11557 01 ', 


1667 


000 


746 




757 


5948 . 545 


1 .0 


0.34 


0.010 


5948 555 


614 


<XX) 


746 




764 


9442.006 


1 .1 


-0.17 


-0.008 


9441 .998 


1186 


(XX) 


746 




766 


19312.904 


1 .0 


-0.04 


-0.003 


19312 901 


57 54 


(XX) 


747 




748 


2997 . 346 


0.7 


1 35 


0.020 


2997 




(XX) 


747 




752 


9626 233 


0.9 


20 


0.009 


9626 242 


1034 


(XX) 


747 




766 


21882.673 


1 .0 


ii ot 


0.005 


21882 678 




(XX) 


748 




750 


2506.212 


0.7 


0.22 


0.003 


2506.215 


924 


(XX) 


748 




757 


4476.773 


0.9 


-0.32 


-0.007 


4471, 


652 


(XX) 


748 




764 


9559.881 


1 .2 


-0.17 


-0.008 


9559.873 


1249 


000 


750 




754 


7081.447 


1.0 


-0.26 


-0.009 


7081 438 


802 


000 


750 




757 


3662.679 


0.8 


-0.08 


-0.002 


3662 677 


2437 


000 


752 




754 


2435.725 


0.5 


0.13 


0.002 


2435.727 


1573 


000 


752 




755 


7283 . 864 


1 .2 


0.21 


0.007 


7283.871 


977 


000 


754 




755 


5042.169 


0.7 


-0 


-0.009 


5042.160 


567 


000 


755 




767 


5237.757 


1.2 


-0.02 


-0.001 


5237.756 


9300 


000 


756 




757 


4488.173 


1 .0 


-0.23 


-0.005 


4488.168 


906 


000 


756 




758 


2311.136 


0.6 


-1 .88 


-0.021 


2311.115 


110 


000 


757 




758 


3564 . 582 


0.9 


0.04 


0.001 


3564.583 


4591 


000 


757 




760 


5123.042 


0.2 


-1.14 


-0.028 


5123.014 


181 


000 


757 




761 


3074.378 


0.7 


-0.98 


-0.015 


3074.363 


211 


000 


758 




762 


3672.189 


0.8 


-0.70 


-0.012 


3672.177 


2% 


000 










STATISTICS 








Number of lengths 


= 116 


Maximum 


positive v 


in seconds = 1 . 52 


Maximum negative v in meters = — . 088 


Maximum 


length 


= 29334.857 


Maximum 


negative \ 


■ in seconds = — 1 . 88 


Average 


length v in meters 


= 0.018 


Minimum 


length 


= 1049.944 


Average length v in 


seconds = 0.45 


The surr 


of pvv in seconds 


= 35 5438 


Average length 


= 9401.455 


Maximum 


positive v 


in meters = 0.096 


The sum 


of vv in seconds 


= 42.0914 



Horizontal Crustal Movements 



289 



Table 7 E.— Adjustment 3 adjusted positions of preearthquake survey stations i 





Geographic position 


Plane coordinates- 


-Zone VII 


Station nur 










Latitude 


Longitude 


X 


Y 




o / n 


O / tl 


Feet 




01 


34 08 24.13961 


118 38 41.07658 


4092458.71 


4163510.65 


02 


34 07 43 . 28089 


118 30 42.98940 


4132637.81 


4159283.95 


03 


34 15 25.40198 


118 38 22.90715 


4094113.76 


4206090.23 


04 


34 20 14.88248 


118 27 15.52227 


4150169.16 


4235236.41 


05 


34 17 33.37499 


118 24 19.55582 


4164914.38 


4218895.68 


06 


34 17 21.86922 


118 27 40.66543 


4148038.70 


4217749.10 


07 


34 18 19.67079 


118 25 58.17186 


4156644.51 


4223582.65 


08 


34 19 30.09626 


118 25 51.38251 


4157220.89 


4230701.41 


09 


34 17 30.02648 


18 29 14.32800 


4140180.84 


4218584.57 


10 


34 15 27.78229 


118 31 10.81051 


4130384.65 


4206243 . 33 


11 


34 17 14.47188 


18 32 23.72430 


4124286.09 


4217040.23 


12 


34 18 42.15401 


118 31 58.45628 


4126423.68 


4225899.75 


13 


34 19 12.75478 


118 33 53.40370 


4116788.15 


4229013.53 


14 


34 14 44.19126 


118 29 16.78522 


4139949.27 


4201820.79 


15 


34 15 48.73113 


18 24 26.62380 


4164313.67 


4208317.75 


16 


34 21 11.67440 


18 24 58.73755 


4161644.76 


4240966.08 


17 


34 08 13.09229 


18 19 29.67663 


4189241.55 


4162250.29 


18 


34 12 54.48116 


18 16 44.67235 


4203C96 . 66 


4190699.35 


19 


34 09 48.84773 


18 11 45.00457 


4228288.72 


4171957.80 


20 


34 13 25.51123 


18 03 38.66780 


4269098.69 


4193941.78 


21 


34 16 08.38729 


18 14 17.09732 


4215472.06 


4210310.08 


22 


34 20 55.42368 


18 13 41.74947 


4218408.91 


4239329.42 


23 


34 22 31.89249 


18 10 28.65017 


4234585.12 


4249102.46 


24 


34 22 54.69098 


18 02 01.25878 


4277109.58 


4251502.66 


25 


34 22 54.69098 


18 02 01.25878 


4277109.58 


4251502.66 


26 


34 30 06.10181 


18 06 02.79338 


4256765.53 


4295062 . 38 


27 


34 23 12.65721 


18 11 01 .76443 


4231803.33 


4253219.23 


28 


34 31 50.26551 


18 08 50.24486 


4242730.92 


4305564.06 


29 


34 32 51.69838 


18 12 52.65141 


4222441.58 


4311744.37 


30 


34 27 35 . 29528 


18 13 04.37738 


4221496.84 


4279756.61 


31 


34 23 10.27113 1 


18 19 02.69884 


4191495.16 


4252945.36 


32 


34 23 10.87286 1 


18 19 43.78944 


4188051.23 


4253005.84 


33 


34 33 37.91345 1 


18 21 18.24926 


4180147.79 


4316396.45 


34 


34 33 39.50178 1 


18 21 18.45949 


4180130.24 


4316557.03 


35 


34 35 58.91362 1 


18 23 49.57592 


4167499.68 


4330656.42 


36 


34 34 01.29103 1 


18 24 42.64990 


4163053.47 


4318768.23 


37 


34 35 54 . 58802 1 


18 27 08.84838 


4150839.69 


4330234.04 


38 


34 33 24.32481 1 


18 28 11.78951 


4145557.32 


4315049.51 


39 


34 35 11.67289 1 


18 31 22.09951 


4129659.18 


4325927.44 


40 


34 32 44.07289 


18 29 56.70540 


4136775.13 


4310993.21 


41 


34 32 00.69314 1 


18 32 17.12277 


4125019.72 


4306629.03 


42 


34 31 02.85169 1 


18 30 52.32691 


4132103.95 


4300768.13 


43 


34 29 52.17461 1 


18 33 00.98687 


4121322.14 


4293644.06 


44 


34 29 29 . 1 7076 


18 31 03.91028 


4131117.51 


4291299.24 


45 


34 28 45.12859 1 


18 33 56.59366 


4116652.30 


4286876 . 36 


46 


34 27 45.56265 


18 32 23.74002 


4124413.88 


4280837.91 


47 


34 27 50.60979 1 


18 34 21.38470 


4114563.86 


4281369.66 


48 


34 26 15.71070 ] 


18 32 31.67048 


4123731.23 


4271755.86 


49 


34 25 46.76662 


18 34 47.40939 


4112354.43 


4268855.19 


50 


34 24 58.91915 1 


18 32 21.39283 


4124576.44 


4263991.07 


51 


34 23 38.46694 1 


18 34 56.13271 


4111592.06 


4255886.90 


52 


34 23 39.29217 1 


18 32 04.87640 


4125944.36 


4255938.68 


53 


34 21 21.89333 1 


18 35 24.06873 


4109216.17 


4242086 . 34 


54 




18 31 11.00308 


4130425.97 


4237725.45 


55 


34 22 30.96253 1 


18 32 06.97252 


4125755.03 


4249031.49 


56 


34 21 08.05919 1 


18 25 43.10281 


4157924.58 


4240603.86 


57 




18 36 00.20378 


4106161.51 


4232522.83 


58 




18 36 00.57377 


4106131.12 


4232769.64 


59 


34 31 57.06340 


18 28 39.91690 
18 40 03.80624 


4143192.15 
4085929.46 


4306231.00 


60 




4293189.64 


61 




18 44 30.62725 


4063699.22 


4319154.48 


62 


34 34 03.16406 


18 44 30.86513 
18 34 43.89321 


4063679.49 
4112794.18 


4319194.66 


63 


34 35 43.94435 1 


4329225.94 


64 




18 33 37.71534 


4118406.05 


4364738.88 



'The geographic position of station Cahuenga 2, No. 17, is adjusted to North American Datum of 1927. All other stations depend on 
this position. 



2!)0 



San Fernando Earthquake of I'>1 1 



Table 7F.— Adjustment l adjusted poHttoru «/ pottearthquake sumry ttattom 



graphii position Plane coordinate / ■ V'lJ 

Station number 

Latitude Longitude X Y 

" ' " ' " i„i 

701 34 00 24.13961 118 38 41 07'.',;: 4092458 71 4163510 63 

702 34 07 43.64 1 72 I If) 30 4 1 02507 41 12634 87 4159320 43 

703 34 15 25.40323 1 18 18 22 91 15 1 4094 1 1 3 40 42000V/ 

704 34 20 14.87885 1 18 27 1 5 53307 4150168 26 1235236 04 

705) 54 17 33 38834 I 18 24 19 6 M 4164907 4218897 03 

706 34 17 22.29286 II8 27 4O.155O0 4148081 4217791.88 

707 34 18 19.67347 1 18 25 58 21440 4150040 94 422 

709 34 17 30.02590 118 29 14 '.1077 4140179 77 4218584.51 

710 34 15 27.78861 118 31 10.81001 4130384.69 4206243.97 

711 34 17 14.47574 118 32 23.72830 41242!)-, 7<, 4217040.62 

712 34 18 42.15492 118 31 00 40224 4126423.18 4225899.84 

713 34 19 12 Ml 744 118 33 51 38619 4116957 4229010 48 

715 34 15 48 74700 118 24 26.61830 4104)14 I) 4208319 

717 34 08 13.09229 118 19 29.67663 4189241 4162250.29 

718 34 12 52.92490 118 16 49.68354 4202675.89 41905418] 

719 34 09 48.84773 118 11 45 00457 422M288 72 4171957 80 

720 34 13 2128507 118 03 42.05349 420881552 4193513.87 

721 34 10 08.38708 11814 I7 09 5HO 4215472 50 421051012 

724 34 22 54.69098 118 02 0125878 4277109.58 4251502.66 

726 34 27 35.11422 118 13 04.13501 4221517 1', 4279750 

727 34 23 12.05001 118 1101700',) 4251802 90 4255219 17 

729 34 32 51.69838 118 12 52 05141 422244158 4511744 

730 34 27 3.5 29245 118 15 04 47727 4221490.85 427 

731 34 23 10.20528 118 19 02 09851 4191495 21 4252944.76 

732 34 25 10.80671 118 1945 79158 4188051.05 4253005.22 

733 34 33 37.91345 118 21 18 24920 4180147.79 4510590.45 

734 34 33 39.50178 118 21 18.45949 4180130.24 4310557 05 

735 34 20 39.20851 118 31 11.00916 4130425.46 4257725 27 

736 34 19 46.09204 1 18 35 59 05661 4106257.42 4252409 29 

737 34 19 49.65471 118 30 00 57912 410*, 150 07 4232769.77 

738 34 2108.04728 118 25 45 11578 415702: 4240002.66 

739 34 22 30.96349 118 32 00 97820 4125754.55 4249031.59 

740 34 21 21 89541 118 35 24.07356 4109215.76 4242080.55 

741 34 23 39.29310 1 18 52 04.88288 4125943.82 4255938.78 

742 34 23 38.46938 118 34 56.13761 4111591.65 4255887.15 

743 34 24 58.91929 118 32 21.39755 4124576.05 4203991 .09 

744 34 25 46.76872 118 34 47.41332 4112354.11 68855.40 

745 34 26 19.78918 118 32 29.50617 4123913.36 4272167.80 

746 34 27 50.61019 118 34 21.38784 4114563.59 4281369.70 

747 34 27 45.56396 118 32 23.74223 4124413.70 4280838.05 

748 34 28 45.13038 118 33 56 59600 4116652.10 4286876.54 

749 34 29 29.17233 118 3103 91240 4131117.33 4291299.40 

750 34 29 52.17644 118 33 00.98833 4121322.02 4293644.25 

751 34 3102.85285 118 30 52.32870 4132103.80 4500768.25 

752 34 3157.06443 118 28 39.91483 4143192.33 4 506231.10 

753 34 33 24.32606 118 28 11.78998 4145557.28 4315049.64 

754 34 32 44.07402 118 29 56.70721 4136774.98 4310993.32 

755 34 35 11.67289 118 3122.09951 4129659.18 4325927.44 

756 34 32 00.69414 118 32 17.12362 4125019.65 4306629.13 

757 34 3101.29187 118 34 57.80295 4111561.44 4300653.76 

758 34 32 35.80765 118 33 37.20996 4118326.97 4310193.11 

759 34 33 46.16086 118 32 48.70733 4122399.44 4317296.77 

760 34 30 06.68429 118 38 07.49414 4095671.16 4295176.12 

761 34 3120.21003 118 36 56.15264 4101662.86 4302592.08 

762 34 32 37.32409 118 36 01.21408 4106280.39 4310375.57 

763 34 34 40.92227 118 34 51.89358 4112109.84 4322856.22 

764 34 29 46.73421 118 40 0.5 80624 4085929.46 4293189.64 

765 34 34 03.16406 118 44 30.86515 4003679.49 4319194.66 

766 34 34 02.76744 118 44 30.62725 4063699.22 4319154.48 

767 34 35 43.94435 118 34 43.89321 4112794.18 4329225.94 

768 34 4135.34140 118 33 37.71534 4118406.05 4364738.88 

1 The geographic position of station Cahucnga 2, No. 717, is adjusted to North American Datum of 1927. All other stations depend on 
this position. 



Horizontal Crustal Movements 



291 



Table 8C— Adjustment 3 position shifts referred to station Cahuenga 2 



Station 



Postearthquake minus preearthquake 



Resultant vector 



AX 


AT 


L 


Azimuth 


Feet 


Feet 


Feet 


o 


-0.33 


+0.39 


0.51 


140 


-0.15 


+0.11 


0.19 


125 


-0.20 


+ 0.18 


0.27 


130 
























-0.36 


+ 0.13 


0.38 


110 


+0.04 


+ 0.64 


0.64 


185 


+0.18 


+0.10 


0.21 


240 


-0.18 


+ 0.14 


0.23 


130 


-0.51 


-0.18 


0.54 


70 


-0.48 


+0.10 


0.49 


100 
























-0.04 


+0.13 


0.14 


io5 


-0.41 


+0.25 


0.48 


120 













-0.27 


+0.04 


0.27 


ioo 


+0.05 


-0.60 


0.60 


355 


-0.92 


-1.20 


1.51 


40 


-0.50 


+0.09 


0.51 


100 


-0.43 


-0.06 


0.43 


80 


-0.54 


+0.10 


0.55 


100 













+0.17 


-0.50 


0.53 


340 


-6.75 


+ 1.35 


6.88 


100 


+0.46 


+ 1.61 


1.67 


195 


+0.01 


-0.28 


0.28 



























-0.45 


+0.13 


0.47 


95 


-0.18 


-0.62 


0.65 


15 


-0.07 


+ 0.10 


0.12 


145 













-1.07 


-0.06 


1.07 


85 


-0.15 


+0.12 


0.19 


130 


-0.39 


+0.02 


0.39 


95 













+0.30 


+0.04 


0.30 


160 


-0.12 


+0.19 


0.22 


150 


-0.90 


-0.37 


0.97 


70 


-3.57 


+0.28 


3.58 


95 


-0.41 


+0.21 


0.46 


115 


+0.17 


-0.06 


0.18 


290 


-0.18 


+0.16 


0.24 


130 



































-0.32 


+0.21 


0.38 


125 



Bluff 

Brushy 

Bum 

Cahuenga 2 

Calabasas 

Chatsworth 

Corner 2 

Deer 

Dry 

East 

Edison 

Flint 

Hauser 

House 

Lock 

Loma Verde 

Long 

Magic 

May 

Mission Pt 

Mt. Gleason 

Newhall 

Pacifico 

Pacoima E-2 ECC 1 

Pacoima L-l 

Pacoima No . 2 

Parker 

Pelona 

Pelona ECC 2 

Pico L-9 AUX 2 ECC 1 

Port 

Powerhouse 

Red 

Reservoir 

Rock 

Saugus 

Sawmill 

Sister Elsie 

Steer 

Sylmar F-8 

Sylmar 1-12 

Towsley 

Verdugo AUX 

View 

Warm Springs 

Whitaker 

WPK A-7A AUX 1 

Yucca 



292 San Fernando Earthquake of 1 971 



Table 9H.— Adjustment J 95-percent error ellipses referred to station (.ohuen^u 2 



Ax'-s [Feel) 



Station One Si^ma 

at 

Bluff 0. 30 

Bum .48 

Cahucnga 2 

Chatsworth 36 

Comer 2 .28 

Deer .50 

Dry .45 

East 

Edison .36 

House .52 

Lock .41 

Long .47 

Magic .31 

May .29 

Mission Pt .31 

Newhall .38 

Pacoima E-2 ECC 1 .25 

Pacoima L-l .23 

Pacoima No. 2 .20 

Parker .40 

Pico L-9 AUX 2 ECC 1 .37 

Port .31 

Powerhouse .52 

Red .57 

Reservoir .26 

Rock .49 

Saugus .40 

Sister Elsie .20 

Steer .49 

SylmarF-8 .29 

Sylmar 1-12 .25 

Towsley .38 

Verdugo AUX .14 

View .47 

Yucca .44 

t Semimajor axis. 
t Semiminor axis. 
* Angle of orientation is measured positive counterclockwise from east. 



95 j,' 



14 



at 



bj 



of b'-niiiJiajMr 



10 
.17 


.17 
.18 
.16 
.17 
.15 
.16 
.16 
.17 
.17 
.14 
.14 
.16 
.16 
.14 
.15 
.15 
.17 
.16 
.14 
.16 
.14 
.15 
.17 
.16 
.14 
.17 
.18 
.17 
.16 
.12 
.17 
.17 



73 
1.17 


89 
68 

1 .22 
I 10 

80 

I .27 

l 01 
1.15 

.70 

.70 

.75 

.93 

.60 

.57 

.49 

.98 

.90 

.77 

1.27 

1.38 

65 

1.20 

.99 

.48 

1.20 

.71 

.02 

.94 

.34 

1.14 

1.08 



I 4<J 
42 

I 

.41 
4', 
40 
42 
17 

.41 
.42 

A 

(8 
.39 
.35 

(6 
.36 
.41 
.39 
.35 
.39 
.35 

17 
.41 
.40 
.35 
.42 
.43 
.41 
.40 
.29 
.43 
.42 



'A 

70 
02 
18 
S3 

42 
41 
17 
44 
16 
1 
24 
49 
M 
40 
20 
27 
104 
55 
3 
27 
21 
43 

37 
151 
31 
34 
31 
50 
171 
28 
40 



Horizontal Crustal Movements 293 



765 a 



766 



764. 



APPARENT HORIZONTAL DISPLACEMENT 



768. 



Scale for Vectors and Ellipses 
12 3 4567 Feet 

1 2 Meters 



5 Miles 5 10 Kr 



767^ 



i^r? 



\<^j£> 



734 




729 



Qt^o 



/727 



(T)721 



701 



702 



718© 



717 

A 
CAHUENGA 2 
( Held Fixed ) 



719 



724 



^720 



Figure 2C. — Adjustment 3 position vectors and 95-percent error ellipses referred to station Cahuenga 2. 



Vertical Crustal Movements 
Determined From Surveys 
Before and After 
San Fernando Earthquake 



CONTENTS 

Page 

295 Introduction 

295 Preearthquake and Postearthquake 

Level Net 

297 Adjustment 

297 Error Propagation 

298 Results 

304 Conclusions 

305 Acknowledgments 
305 References 

305 Appendix — Tables of Observed 
Elevation Differences 



NANCY L. MORRISON 

National Geodetic Survey 
National Ocean Survey, NOAA 



INTRODUCTION 

The earthquake which struck the San Fernando 
area on the morning of February 9, 1971, caused 
widespread surface ruptures. The main concern of 
this paper is not with the actual breaks in the sur- 
face, which can take place only along a fault, but 
rather with the widespread vertical deformations re- 
sulting from the shock waves. The magnitude and 
extent of vertical crustal movement, determined by 
comparing the results of leveling surveys before the 
earthquake with those of special surveys after the dis- 
turbance, are described in this paper. 

PREEARTHQUAKE AND POSTEARTHQUAKE 
LEVEL NET 

The area of general interest is shown in figure 1. 
Awareness of earth movement as an ongoing process 
in several areas of southern California led to a com- 
prehensive leveling program during the period from 
January 31, 1968, to December 5, 1969, undertaken 
by the National Geodetic Survey (NGS) of the 
National Oceanic and Atmospheric Administration 
(NOAA) , by San Bernardino, San Diego, Los 
Angeles, Orange, Riverside, and Ventura Counties, 
and by Los Angeles city. All leveling was first-order 
work, with a rejection limit of 3 mm V~K, where K is 
the distance in kilometers. 

At the time of the earthquake, an NGS leveling 
party was working in the vicinity of Point Mugu on 
a line from Santa Margarita to San Pedro. The line 
was finished and then portions were releveled to 
make certain there were good ties between pre- 



295 



2 l M) San Fernando Earthquake of 1971 




Figure 1. — Level net for study of San Fernando earthquake, with indication of 1972 misclosures in mm. km. 



Vertical Cruslal Movements 



29> 



earthquake and postearthquake level ings. The re- 
sources of NGS, Los Angeles city, and Los Angeles 
County were used to relevel enough lines of the 
1968-69 net to provide information for the study of 
possible widespread crustal disturbances as a result 
of the earthquake. This program consisted of 1,080 
km of releveling, plus 88 km of original leveling 
done between February 9, 1971, and December 15, 
1971. A total of 1,162 marks were recovered. Again, 
all leveling was 3-mm V~K first-order. The area is 
covered by 10 major loops, as shown in figures 1 and 
1A with their misclosures. In addition, there are 28 
minor loops. Figure 1A shows the loop misclosures 
in the vicinity of Saugus. All exceed the 3-mm V7C 
limit. These lines were run within a 3-month period, 
but since there were aftershocks occurring during this 
time, it is impossible to determine whether the dis- 
agreement is caused by actual movement or by an 
error in leveling. It should be noted that the resultant 
of the three misclosures is well within the 3-mm VT( 
limit. 

ADJUSTMENT 

Preliminary reduction of data included computa- 
tion of temperature and rod corrections, a correction 
for instrument error, and an orthometric correction 
to account for the nonparallelism of level surfaces to 
produce an observed orthometric elevation for each 
mark (henceforth referred to as the observed eleva- 
tion) . 

Independent free adjustments for each epoch of 
leveling were made using the variation of parameters 
method of least squares. In a free adjustment, the net 
is not constrained to fit previously established eleva- 



tions. A single mark is assumed stable at a fixed ele- 
vation, and all other elevations are adjusted in rela- 
tion to it. Therefore, any comparison of the 
free-adjusted elevation of a mark in one epoch to 
that of a second epoch with the same fixed point in- 
dicates apparent movement between the two level- 
ings. Bench Mark Tidal 8 at San Pedro (El. 3.3924 
m) , considered stable by oceanographers, is the fixed 
point in each case. The adjustment of 1970 includes 
134 unknowns and 198 links; the 1972 adjustment 
consists of 67 unknowns and 104 links. The weisrht 
of a link is expressed as 



Wi = 



tDi 



where D; is the distance associated with the *th 
observation and t is a constant of proportionality 
reflecting the precision of the observation. Because 
all leveling was 3-mm V K first-order, as a matter of 
convenience, t was chosen to be equal to unity for 
each link. 

The adjustments yielded the following results: 



1970 1972 
Standard deviation of an obser- 
vation of unit weight ' 1 .86 1 .75 

Average correction rate 0. 187703 0.204302 



Unit of 
measurement 

mm 
mm /km 



The results for all recovered marks are tabulated 
in the appendix, and after allowing for propagation 
of the error that results from leveling, they may be 
considered to reflect the magnitude of the move- 
ments. Movement is calculated as the 1972 free-ad- 
justed elevation minus the 1970 free-adjusted eleva- 
tion. A plus sign ( + ) , therefore, indicates uplift, 
while a minus sign ( — ) indicates subsidence. Eleva- 
tions are not to be considered as absolute, but only 
as based on Bench Mark Tidal 8 at San Pedro. 







£ 



ERROR PROPAGATION 

In a large net, such as described here, only a small 
percentage of the total number of bench marks is 
used as unknowns in the adjustment. An adjusted 
elevation is computed for each unknown, and an 
associated standard deviation may be computed from 
the covariance matrix. To determine the adjusted 
elevation of an intermediate bench mark, pi, lying 
on a level line between two bench marks, p A and p B , 



Figure 1A. — Detail of misclosures (mm /kin) in vicinity of Saugus. 



i An observation of unit weight is a double-run difference of 
elevation obtained over a distance of 1 km. 



298 San Fernando Earthquake of 1971 



which are unknowns in the adjustment, the following 
weighted mean is used: 



Hi = -^-(H A +*Ai) +t4-(# « +*Bi) 



(1) 



S1+S2 Sl+S 2 

where 

H A is the adjusted elevation of p A , 

l A < is the observed difference of elevation from 

Pa to pi, 
H B is the adjusted elevation of p B , and 
Ibx is the observed difference of elevation from 
Pb to p t ; 
and the respective weights are determined as follows: 

_1_ 

uh_ _ _ tsi S2 

[Wi 



\tSi tSiJ 



•*!+*! 



where 

Si is the distance from p A to pi, 
s 2 is the distance from p B to p t , and 
/ is equal to unity as explained previously, and 
similarly, for Wi . 

M 

The apparent movement, M 4 , of point p; is calcu- 
lated as the 1972 free-adjusted elevation, H'i, minus 
the 1970 free-adjusted elevation, H it so that 

Mi=H' i —H i , 

and an associated standard deviation, ffM is found by 



a Mi= J*' a i t + 9B t . (2) 

Covariances are not involved because the old and 
new adjusted levelings are independent. 

Applying the laws of error propagation (Hirvonen 
1971) to equation (1) and knowing the variances of 
the end points of a link, p A and p B , we have 



^1+^2 



f-s-Y- 

\Sl+St/\S 



-V 



(3) 



and similarly for a H ) .. 

However, because of the shortage of time between 
the receipt of data from the field and the publication 
deadline of this volume and because of the necessity 
of manually computing these tr's, standard deviations 
have been calculated for only a representative sample 
of points. This includes all points occurring as junc- 
tions in both adjustments, for which standard devia- 
tions are available from the covariance matrix, and 



various intermediate points for whirh the linen 
interpolation equation (4) , 



* Si-ri2 



(A) 



was used as an approximation in place of equation 
(3). 

RESULTS 

Because of the short interval of time between the 
preearthquake and postearthquake leveling, the re- 
sulting evaluation of displacements should reflect, for 
the most part, only movements caused directly by the 
earthquake. Awareness of persisting crustal move- 
ment was a basic reason for the comprehensive level 
net of 1968-69; thus, in any analysis of apparent 
movement, an attempt must be made to separate 
this tectonic movement from the abrupt elevation 
changes that result from seismic activity. Several 
areas in California are known to undergo subsidence 
where, for various reasons, there is a widespread low- 
ering of the land surface with respect to mean sea 
level, caused by compaction of sediments CHoldahl 
1969 and 1970) . This subsidence is a relatively slow 
process and generally remains undetected without re- 
peated surveys until enough small movements have 
accumulated to cause noticeable property damage. In 
contrast, there are no zones of definite upheaval as 
would be associated with mountain building, but 
past leveling has indicated that such areas may exist. 
Where continual small movements are indicated, 
caution must be used before any cause-and-effect re- 
lation is established. 

In addition, it is possible that in a statistical, 
least-squares solution, the standard deviations may 
sometimes exceed the effects of small, real earth 
movements. For this reason, movement is considered 
to be significant if it consistently exceeds a- rather 
than the 2 a required for a 95-percent confidence 
interval. 

Portions of lines in the net, indicating significant 
movement, are shown in figure 2. Each line segment 
is labeled with the number of the figure in which a 
graph of the movement will be found. To avoid con- 
fusion, some graphs contain only representative 
points. Detail of significant movement, such as uplift 
and subsidence, is shown in figure 2A. 

An area of definite vertical displacement begins in 
the vicinity of Sun Valley (fig. 3) at BM 08-25620 



Vertical Cruslal Mox/emcnls 299 



^PoM Hueneme 



Caslaic Junction 

f Saugus 




Granada Hills Pac 



Woodland Hills 




•jRedondo Beach 



I s, iMmm*. 



Sk 



Figure 2. — Portions of leveling lines along which significant movement occurred. 
Graph of apparent vertical displacement along line is shown in indicated figure. 



.-500 San Fernando Earthquake <>\ I ( J7I 





Sanl » Mo» ■ s 





Ange e 




[ I Subsidence . . ' : ..'"'^'.' .' : 

ggg^g uplift ' ; ' ; ^;;'1PI^III 

Figure 2A. — Detail of significant movement shown as uplift or subsidence. 



Vertical Crustal Movements 301 



600 -i 



500- 



400- 



300- 



200- 



100- 



0- 



100 - 1 




Figure 3. — Graph of apparent vertical displacement: 1972 free-adjusted elevation minus 1970 free-adjusted elevation. Standard deviation for 
these displacements varies from 14 mm at Sun Valley to 16 mm jwrth of Van Norman Lake. Distance is calculated in km from 
Tidal Bench Mark 8 at San Pedro. 



302 



San Fernando Earthquake of 1971 



(City of Los An«des — C oi LA). The apparenl 
movement here is — 23 mm, a — 14 mm. This sub- 
sidence increases in magnitude to a sustained 

- 63 mm, a = 15 mm, at BM 03-01685 (C oi LA), 
BM ().'}-0I687 (C of LA), and BM 03-01710 (C oi 
LA) . Then follows a decrease in movement to 

- 41 mm, a = 15 mm, at I5M N 898 = 03-01930 
(C of LA) and BM 03-01950 (C of LA) in the 
vicinity of Pacoima, and another increase in magni- 
tude to — 69 mm, <j = 15 mm, at BM S 43 Reset 
I960 = 03-02251 (C of LA) . A second decrease in 
magnitude occurs from this point to BM 03 02429 
(C of LA), with apparent movement of — 21 mm, 
a = 15 mm. At a distance of 0.2 km farther, 
BM 03-02440 (C of LA) shows an uplift ol 
+ 29 mm, (7=15 mm. This is the beginning of a 
zone of sustained uplift over a 15-km section of north- 
south leveling located a short distance to the east oi 
Van Norman Lake. A mark-by-mark tabulation of the 
displacements to a maximum of + 615 mm, 
o- = 15 mm, will be found in table 1 of the appendix. 
The apparent movement decreases to the noise level 
at BM 60-30A (CSDH) . This displaced region has 
a maximum extent of 29 km. 

A second area of definite vertical displacement 
begins in the vicinity of Granada Hills (fig. 4) . The 
apparent movement is consistently within a over the 
line from Topanga Creek to Granada Hills where 
BM 04-05610 (C of LA), showing an uplift of 
+ 37 mm, a = 16 mm, is the beginning of the most 
dramatic area of upheaval in the region under study. 
This 27-km section runs in an east-west direction 
from Granada Hills, passing a short distance south of 
the Olive View Sanatorium and north of Hansen 
Lake to Tujunga. The maximum movements occur 
at BM 03-00780 (C of LA) and BM 03-00770 
(C of LA) , having displacements of + 1,460 mm, 
o- = 16 mm, and + 1,510 mm a = 16 mm, respec- 
tively. This maximum uplift area is folloAved within 
2.5 km by a zone of fairly large downthrusts which 
degenerate to the noise level at BM 02-03900 (C of 
LA) . A mark-by-mark tabulation of these displace- 
ments will be found in table 3. Considering figures 
3 and 4 together gives an area of subsidence to the 
east and south of the vicinity of Van Norman Lake 
and a region of uplift to the west and north. 

Figure 5 shows an area of probable upheaval be- 
ginning at BM RV 64 (SPRR) = 208-83 (Los 
Angeles County — LACo) near Castaic Junction, with 
apparent movement of + 30 mm, <r = 18 mm. This 
increases to + 64 mm, <, = 18 mm, at BM 208-89 



(LACo) neai Saugus and reaches a maximum about 
10 km north ol Saugus ol •}- HJ mm, o — 18 mm, at 
BM 201 II I A (LA< o Foi the nexi 38 i m, the 
releveling program followed a route different from 
that ol the 1968 69 nei consequently, then 
marks available for comparison. However, where the 
releveling line rejoins the old hue, continued uplift 
is indicated, and one may assume an average move- 
ment ow-i the- uncompared section of approximately 
+ 90 mm, » = 20 mm. As the line passes through 
Palmdale, the apparenl displacement dec leases in 
magnitude and changes sign. BM S *ll Reset 
1955 - 101 127 (- 37 mm, „ = 23 mm, is the be- 
ginning ol a vigorous downthrust continuing to 
- 140 mm, a - 2.3 mm, at BM 2356 USGS) = 
101-111 \. I his magnitude decreases to a fairly con- 
stant — 90 mm, a = 23 mm, for the next 10 km and 
then decreases rapidly to — 38 mm, a = 23 mm, at 
BM M 187 = 101-151 which is the end of the level- 
ing line 6.9 km south ol Rosamond. 

It should be noted at this point that previous level- 
ing in the Palmdale-Rosamond vie inky indicates that 
the area is gradually subsiding. It is possible, there- 
fore, that the uplift near Saugus is related to the 
earthquake, but that the subsidence between Palm- 
dale and Rosamond is a continuing process, totally 
unaffected by the earthejuake or only slightly so. 

A second area of probable uplift (fig. 6) begins 
about 9 km south of Gorman at Quail F RM 1 = 
102-82B (LACo) . showing an apparent displacement 
of +31 mm, <t = 23 mm. This displacement in- 
creases gradually in magnitude to +51 mm, 
o- = 25 mm, at BM S 1098 near Grapevine. The re- 
leveling ends 4.8 km north of Grapevine, with a 
gradual decrease in magnitude indicated. Again, 
previous leveling in the area indicates small con- 
tinued movements, and cause-and-effect relation with 
the earthquake cannot be established. 

The vicinity of Point Mugu-Lechusa Point (fig. 7) 
is an area of possible subsidence. From BM M 1099, 
10 km east of Port Hueneme, to BM F9A = 48-102, 
near Lechusa Point, the apparent movement remains 
fairly constant around — 32 mm, while a varies from 
20 to 18 mm. Past leveling indicate that this mav be 
a moving area. If future leveling verifies this con- 
clusion, it would be doubtful that the area has been 
affected by this earthquake. 

The final section of leveling: showing significant 
movement lies between BM 21-03910 (C of LA), 
located 22 km north of San Pedro, and BM 12-01329 
(C of LA) , about 4 km south of the Los Angeles 



Vertical Cruslal Movements 303 



1600 n 



1400- 



1200- 



1000- 



800 



600- 



400- 



200- 



0- 




200 



1'iguie I. — Graph of apparent vertical displacement: 1972 free-adjusted elevation minus 1970 free-adjusted elevation. Standard deviation 
for these displacements remains a constant 16 mm. Distance is calculated in km from DM P 99 Reset 1933 = 48-62 at Santa Monica. 



304 San Fernando Earthquake "I 1971 







«IO 80 




Figure 5. — Graph of apparent vertical displacement: 1972 free- 
adjusted elevation minus 1970 free-adjusted elevation. Standard 
deviation for these displacements varies from IX mm at Saugus 
to 22 mm at Palmdale to 23 mm at Rosamond. Distance is calcu- 
lated in km from BM H 1051 at Montalvo. 




Figure 6. — Graph of apparent vertical displacement: 1972 free- 
adjusted elevation minus 1970 free-adjusted elevation. Standard 
deviation for these displacements varies from 23 mm south of 
Gorman to 25 mm north of Lebec. Distance is calculated in km 
from Tidal Bench Mark 8 at San Pedro. 



City Hall (fig. 8) . The apparent movement averages 
about — 18 mm. There is one relatively large down- 
thrust to — 40 mm, followed by a fairly rapid return 
to the — 18-mm level. The standard deviation varies 
from 9 to 13 mm at the Los Angeles City Hall. This 
movement is barely significant. Once again, slight 
movements over the years have been indicated in 
this area, and no definite connection with the earth- 
quake can be made. 










; ~-^y ■ 




Figure 7. — Graph of apparent vertical displaremetit 1972 free- 
adjusted dilution minus 1970 free-adjusted elevation. Standard 
deviation for these displnr i ments varies from 20 mm at Foil 
Hueneme to 1H mm at Lechusa 1'omt. Distance is 'ulrulated in 
km from ISM X 569 at Ventura. 







J 



Figure 8. — Graph of apparent vertical displacement: 1972 free- 
adjusted elei'ation minus 1970 free-adjusted elevation. Standard 
deviation for these displacements varies from 9 mm to 13 mm 
at Los Angeles City Hall. Distance is calculated in km from Tidal 
Bench Mark 8 at San Pedro. 



CONCLUSIONS 

Results of the comparison of marks in the 1968-69 
preearthquake net with those in the 1971 postearth- 
quake releveling indicate that earth movements defi- 
nitely caused by the disturbance fall within an 
ellipse, centered on maximum displacement BM 
03-00770 (C of LA) near the Olive Mew Sanato- 
rium, with a major axis of 20 km oriented in a 
northwest-southeast direction and a minor axis of 1 1 
km oriented in a northeast-southwest direction. Areas 
of movement outside this region may have been 
affected by the earthquake, but most likely these are 



Vertical Crustal Movements 



305 



ireas of continuing gradual movement. It so, the 
omparisons are of some use for determining move- 
nent rates in these areas. 

ACKNOWLEDGMENTS 

The author wishes to thank Allen Pope and San- 
ord Holdahl for their conversations on and help 
iith the statistics. 

IEFERENCES 

lirvonen, R. A., "The Propagation of Errors" and "Matrices," 
Adjustment by Least Squares in Geodesy and Photogram- 
metry, Chs. Ill and XII, Frederick Ungar Publishing Co., 
New York, N.Y., 1971, pp. 20-35 and 136-150. 

loldahl, Sanford R., "Geodetic Evaluation of Land Sub- 
sidence in the Central San Joaquin Valley of California" 



(abstract) , EOS Transactions, American Geophysical Union, 
Vol. 50, No. 11, Nov. 1969, p. 601. 
Holdahl, Sanford R., "Studies of Precise Leveling at California 
Fault Sites" (abstract), EOS Transactions, American Geo- 
physical Union, Vol. 51, No. 11, Nov. 1970, p. 742. 

APPENDIX-TABLES OF OBSERVED 
ELEVATION DIFFERENCES 

The following tables contain a mark-by-mark tab- 
ulation of the results of the two adjustments for each 
of the 1,162 recovered marks. A name appearing in 
the column headed "Location" means "in the vicin- 
ity of." Each table is considered as a continuous line 
of levels, and distance is calculated from the first 
mark in the table. Apparent movement is computed 
as the 1972 free-adjusted elevation minus the 1970 
free-adjusted elevation, a is the standard deviation 
of the apparent movement. 



306 



San Fernando Earthquake of 1971 



Table I.— Line of levels, San I'edro to 1.9 km north oj < ', r a fteiiine 



it ion 



Location 



Bench mark 



I h tance 



thquakc Portearthquake 



ureal 
movement 



San Pedro . 



km 

24 0010-Tidal 8 0.00 

24 00030(CofLA) 0.07 

24 00050(CofLA) 0.49 

24-00070(CofLA) 0.84 

24-00090(CofLA) 0.89 

24-001 10 = Tidal 10 0.94 

24-001 30(CofLA) 1 07 

24-O0150(CofLA) 1.54 

24-00 1 70U loll. A) 1.75 

24-O0609(CofLA) 2.04 

24-006 15(Cof LA) 2. It, 

24 00625(CofLA) 2.2 r , 

24-00635(CofLA) 2.36 

24-00650(CofLA) 2 .50 

24-00670(CofLA) 2. 58 

24-00690(CofLA) 2 . 70 

24-00710(CofLA) 2 81 

24-00730(GofLA) 3.04 

24-0()750(CofLA) 3.13 

24-00755(GofLA) 3 . 24 

24-00771(CofLA) 3.45 

24-00773(CofLA) 3.62 

24-00825(CofLA) 3.70 

24-00845(CofLA) 3.82 

24-009 10(Cof LA) 3.93 

24-00930(CofLA) 4.12 

24-00950(CofLA) 4.24 

24-00970(CofLA) 4.36 

24-00990(CofLA) 4.55 

24-01010(CofLA) 4.62 

24-00490(CofLA) 4.65 

24-005 10(Cof LA) 4.68 

24-00590(CofLA) 5.35 

24-01406(CofLA) 6.04 

24-014 10(Cof LA) 6.25 

24-O1430(CofLA) 6.32 

24-01450(CofLA) 6.66 

24-01470(CofLA) 7.11 

24-01490(CofLA) 7.25 

24-01510(CofLA) 7.58 

24-01530(CofLA) 7.76 

24-01550(CofLA) 7.94 

24-01570(CofLA) 8.11 

24-01580(CofLA) 8. 19 

24-01590(CofLA) 8.47 

24-01610(CofLA) 8.50 

24-02580(CofLA) 8.68 

24-02590(CofLA) 8.83 

24-026 10(Cof LA) 9.02 

24-02640(CofLA) 9.23 

24-02650(CofLA) 9.34 

24-02660(CofLA) 9.45 

21-03690(CofLA)=5-46 C 13.61 

21-03693(CofLA) 13.82 

21-03698(CofLA) 14.02 

21-03710(CofLA) 14.26 

21-03731(CofLA) 14.67 

21-03750(CofLA) 15.50 

21-03770(CofLA) 15.95 

21-03792(CofLA) 16.50 

21-03815(CofLA) 18.36 

21-03832(CofLA) 19.12 

21-03850(CofLA) 19.99 

21-03858(CofLA) 20.22 

21-03865(CofLA) 20.45 



m 

', »92 
2.045 
I 969 
3.312 
2.183 

2.779 

II 014 

15 498 

20.871 

21 \<)b 

\<) 549 

14.586 

8 612 

-, 431 

907 
6.515 
t. 500 
6.986 

6.432 

., 990 
4 689 
3.974 
3.467 
3.018 

2.788 
3.132 
3.134 
3.482 
3.790 

3.949 
3.909 
2.855 
5.742 
3.427 

3.766 
3.522 
3.409 
3.248 
2.862 

2.808 
3.086 
2.760 
2.398 
2.700 

2.282 
4.391 
6.556 
8.258 
9.733 

10.063 
10.910 
13.130 
12.587 
12.480 

12.520 
11.307 
10.954 
10.976 
8.765 

6.516 
3.927 
4.585 
5.409 
5.757 



m 

', J92 

2 04 J 
I 964 

3 '.II 
2.181 

2 . 776 

4 568 

I I ', I 2 
15 ■Vi'i 
20 870 

21 .195 
19 549 
14 585 

•<: 612 

-> 4 ',0 

-, '*>- 
',014 
o.498 
h 986 
b .428 

4 689 
3.972 
3.466 
3.017 

2.788 
3.133 
3.134 
3.482 
3.791 

3.950 
3.910 
2.856 
5.743 
3.430 

3.769 
3.522 
3.406 
3.243 
2.854 

2.799 
3.077 
2.749 
2.383 
2.685 



2.267 
4.374 
6.536 
8.234 
9.709 



10.038 
10.883 
13.108 
12.568 
12.463 

12.505 
11.294 
10.948 
10.970 
8.762 



511 
913 
584 
407 
759 



mm 



-2 

-5 

-I 

-2 

-3 

-4 
-2 
4-1 

-1 

-I 
(J 

-1 
o 

-1 



-1 

-2 


-4 





-2 

-1 

-1 


+ 1 




+1 

+1 

+1 
+1 
+1 

+3 

+ 3 

-3 
-5 
-8 

-9 

-9 

-11 

-15 

-15 

-15 
-17 
-20 
-24 
-24 

-25 
-27 
-22 
-19 
-17 

-15 
-13 

-6 
-6 
-3 

-5 
-14 

-1 

-2 
+2 



mm 

o 



Vertical Craslal Movements 



30/ 



Table I.— Line of levels, San Pedro to 4.9 km north of Grapevine— Continued 



Location 



Bench mark 





Elevation 


Apparent 


Distance 






movement 








Preearthquake 


Postearthquake 




km 


m 


m 


mm 


20.85 


6.512 


6.507 


-5 


21.47 


13.986 


13.980 


-6 


22.04 


12.851 


12.841 


-10 


22.50 


15.734 


15.721 


-13 


22.77 


14.704 


14.690 


-14 


23.24 


16.372 


16.358 


-14 


23.69 


17.531 


17.515 


-16 


24.46 


23.816 


23.797 


-19 


24.75 


26.917 


26.897 


-20 


25.19 


30.144 


30.123 


-21 


25.57 


35.489 


35.470 


-19 


26.05 


36.749 


36.729 


-20 


26.38 


35.935 


35.917 


-18 


26.77 


36.383 


36.362 


-21 


27.21 


35.054 


35.032 


-22 


27.66 


35.543 


35.523 


-20 


28.05 


36.007 


35.987 


-20 


28.25 


36.014 


35.995 


-19 


28.88 


33.226 


33.210 


-16 


29.20 


32.899 


32.883 


-16 


29.73 


34.533 


34.517 


-16 


30.13 


34.663 


34.646 


-17 


30.59 


36.168 


36.151 


-17 


30.82 


36.516 


36.499 


-17 


31.14 


37.121 


37.103 


-18 


31.54 


37.961 


37.944 


-17 


31.85 


38.521 


38 . 502 


-19 


32.26 


40.043 


40.024 


-19 


32.70 


40.873 


40.833 


-40 


33.12 


41.453 


41.421 


-32 


33.33 


41.906 


41.875 


-31 


33.93 


43.940 


43.911 


-29 


34.32 


45.134 


45.106 


-28 


34.84 


47 . 705 


47.681 


-24 


35.17 


48.859 


48.839 


-20 


35.67 


50.537 


50.518 


-19 


36.12 


51.128 


51.110 


-18 


36.50 


52 . 594 


52.574 


-20 


36.95 


53.905 


53.887 


-18 


37.34 


55.496 


55.475 


-21 


37.61 


55 . 905 


55.887 


-18 


38.24 


59.309 


59.292 


-17 


38.53 


60.550 


60.533 


-17 


38.59 


60.794 


60.777 


-17 


39.02 


63.191 


63.173 


-18 


39.52 


64.898 


64.883 


-15 


39.85 


65.962 


65.950 


-12 


40.34 


68.446 


68.438 


-8 


40.60 


69.091 


69.085 


-6 


40.97 


70.885 


70.881 


-4 


41.38 


72.820 


72.814 


-6 


41.81 


74.951 


74.945 


-6 


42.14 


76.141 


76.131 


-10 


42.63 


78.263 


78.249 


-14 


42.81 


79.059 


79.045 


-14 


42.99 


79.662 


79.647 


-15 


43.67 


85.298 


85.287 


-11 


43.90 


87.403 


87.392 


-11 


44.25 


103.397 


103.386 


-11 


44.69 


92.713 


92.698 


-15 


45.41 


87.094 


87.075 


-19 


45.61 


88.497 


88.478 


-19 


46.06 


89.805 


89.785 


-20 


46.37 


90.789 


90.769 


-20 


46.72 


93.273 


93.256 


-17 


46.95 


95.523 


95.507 


-16 



San Pedro (continued) . 



Los Angeles City Hall . 



21-03878(CofLA) 

21-03891(CofLA) 

21-03910(CofLA) 

21-03930(CofLA) 

21-03938(CofLA) 

21-03951(LACo) 

21-03969(CofLA) 

21-03993(CofLA) 

21-0401 l(CofL A) 

21-04020(CofLA) 

1 8-000 12(Cof LA) 

18-00050(CofLA) 

18-00070(CofLA) 

18-00088(CofLA) 

18-00130(LACo) 

18-00140(CofLA) 

18-00170(CofLA) 

18-00209(CofLA) 

1 8-002 70(Cof LA) 

18-00289(CofLA) 

18-00332(CofLA) 

18-00371(CofLA) 

18-00420(CofLA) 

1 8-004 50(Cof LA) 

1 8-0049 l(Cof LA) 

1 8-0057 l(CofLA) 

1 8-006 10(Cof LA) 

18-00650(CofLA) 

18-00670(CofLA) 

1 8-007 10(Cof LA) 

18-00730(CofLA) 

1 8-007 70(Cof LA) 

18-00790(CofLA) 

18-00850(CofLA) 

1 8-0089 l(Cof LA) 

T 412= 18-00930 

18-00969(CofLA) 

18-00990(CofLA) 

18-01069(CofLA) 

A 170=18-01090 

18-01 130(Cof LA) 

18-01 170(Cof LA) 

18-01197(CofLA) 

18-01205(CofLA) 

18-01249(CofLA) 

12-01291(CofLA) 

12-01329(CofLA) 

12-01 370(CofLA) 

12-05749(CofLA) 

12-05760(CofLA) 

12-05791(CofLA) 

1 2-058 10(Cof LA) 

12-05820(CofLA) 

1 2-0584 l(Cof LA) 

12-05862(CofLA) 

12-05866(CofLA) 

12-03330(CofLA) 

12-03350(CofLA) 

S 32 = 338 Reset 1936=12-17190. 

12-19171(CofLA) 

12-04550(CofLA) 

12-04530(CofLA) 

L 141=12-04840 

1 2-048 14(Cof LA) 

V 32= 12-04790(CofLA) 

12-04750(CofLA) 



10 



12 



13 



'M)H 



San Fernando Earthquake of 1971 



Table l.-Line of levels, San Pedro to 43 km north of GfOpex iru ( .,,,< 



Location 



Bench mark 



Los Angeles City I [all 
(continued). 



Sun Valley. 



E 769=12 34910(CofLA) 

12-24970=49 lA(LACo) 

12-24990-9 25(LACo) 

12-25030(CofLA) 

12-25035(CofLA) 

12-25041(CofLA) 

D 99=12-25050 

!2-25074(CofLA) 

N 970 Reset 1967 = 12-25087.. 
l2-25089(CofLA) 

12-25109(CofLA) 

1 2-251 25(Cof LA) 

X 768 Reset 1948 = 12-25065 

12-25135(CofLA) 

12-251 70(CofLA) 

12-25202(CofLA) 

W 768=12-25210 

12-25250(CofLA) 

V 71,8 = 12-25270 

12-24430(CofLA) 

B 52 = 12-22785 

J 32 = 432 (USGS) = 12-22790. 

U 768=12-22810 

09-01 50()(Cof LA) 

09-01530(CofLA) 

T 768=09-01560 

N 1141=09-01605 

09-01620(CofLA) 

09-01650(CofLA) 

E 99 Reset 1935=09-01655. . . 

09-01705(CofLA) 

09-01710(CofLA) 

09-01 720(Cof LA) 

09-01 750(Cof LA) 

09-01 785(Cof LA) 

09-01830(CofLA) 

B 787=09-01840 

Y 60=09-01860 

09-01862(CofLA) 

C 787=09-01891 

H 43 Reset 1932=09-01920. . . 

09-01950(CofLA) 

R 786 = 09-01980 

09-020 10(Cof LA) 

S 786=09-02040 

08-25525(CofLA) 

38-239 = 08-25526 

G 787 = 08-25530 

08-25560(CofLA) 

L 43 Reset 1946=08-25590. . . 

08-25620(CofLA) 

U 786=08-25645 

08-25650(CofLA) 

08-2568 l(Cof LA) 

08-25740(CofLA) 

08-25750(CofLA) 

08-02 190(Cof LA) 

Z 786 = 08-25800 

08-258 15(Cof LA) 

08-25830(CofLA) 

08-25834(CofLA) 

08-25840(CofLA) 

08-25860(CofLA) 

W 786 = 08-25870 

08-25890(CofLA) 







App; 












o 




I'm earthquake 








km 


m 


m 






47.2'5 


96.254 


2 ',•> 


-15 




47.64 


101 477 


101 463 


-14 




48 35 


856 


98 844 


-12 




48 . 5 1 


101 .740 


101 729 


-11 




49.21 


103.730 


103 719 


-11 




49.60 


104 045 


104.032 


-13 




19 94 


104.467 


104 475 


-12 




50. 16 


104.924 


104 91 J 


-11 




50 59 


106 085 


106.074 


-11 




50.85 


107.576 


107. 56 % 


-12 




51 .40 


114.096 


114.085 


-11 




51 .69 


112 .510 


112 500 


-10 




51 .81 


112.437 


112.427 


-10 




52.17 


112 417 


112.409 


-8 




52.71 


I 14 . 1 55 


114.154 


-1 




53.17 


119.749 


119 729 


-20 




53 53 


120.052 


120 049 


-3 




65 


117.720 


117.717 


-3 




54.50 


126.877 


126.864 


-13 




54.85 


127.810 


127.797 


-13 




55.62 


131 .844 


131.830 


-14 




55.70 


1 11.745 


131 .732 


-13 




56 . 36 


134.590 


134.575 


-15 




56.82 


135.039 


135.026 


-1 1 




56.89 


1 J5.745 


135 


-13 




57.41 


1 38 


138.515 


-14 




58 . 1 7 


141. 084 


141 .070 


-14 




58.27 


141.820 


141 .805 


-15 




58.82 


142 690 


142.670 


-14 




58.99 


140.552 


140.538 


-14 




59.58 


141.446 


141.433 


-13 




59.81 


141.539 


141.526 


-13 




60.76 


142.766 


142.751 


-15 




60.79 


143.096 


143.079 


-17 




61.63 


148.953 


148.938 


-15 




63 . 37 


160.559 


160.540 


-19 




63.65 


163.330 


163.310 


-20 




64.66 


172.850 


172.828 


-22 




64.71 


173.070 


173.048 


-22 




65.56 


178.559 


178.541 


-18 




66.02 


182.529 


182.512 


-17 




66.28 


181.568 


181.551 


-17 




66.84 


190.010 


189.994 


-16 




66.95 


190.636 


190.620 


-16 




67.37 


194.989 


194.974 


-15 




68.01 


201.645 


201.630 


-15 




68.22 


204.159 


204.143 


-16 




68.97 


213.600 


213.581 


-19 




69.44 


219.340 


219.319 


-21 




69.71 


222.991 


222.968 


-23 




70.12 


227.544 


227.521 


-23 




70.31 


230.202 


230.175 


-27 




70.37 


229.669 


229.647 


-22 




71.39 


241.530 


241.505 


-25 




71.67 


244.660 


244.636 


-24 




71.97 


247.168 


247.143 


-25 




72.18 


248.621 


248 . 595 


-26 




72.56 


252.355 


252.327 


-28 




73.05 


255.779 


255 . 748 


-31 




73.21 


257.451 


257.420 


-31 




73.30 


258.828 


258.797 


-31 




73.84 


261.663 


261.630 


-33 


15 


74.02 


263.613 


263.579 


-34 




74.10 


264.807 


264.772 


-35 




74.47 


267.400 


267 . 364 


-36 





Vertical Cruslal Movements 



309 



Table l.—Line of levels, San Pedro to 4.9 km north of Grapevine— Continued 



Location 



Bench mark 



Distance 


Elevation 


Apparent 
movement 








Preearthquake 


Postearthquake 




km 


m 


m 


mm 


74.52 


267.660 


267.623 


-37 


74.93 


271.139 


271.098 


-41 


75.13 


272.597 


272.553 


-44 


75.39 


274.327 


274.280 


-47 


75.86 


276.274 


276.222 


-52 


75.88 


276.843 


276.791 


-52 


76.10 


280.376 


280.322 


-54 


76.29 


279.353 


279.298 


-55 


76.78 


278.878 


278.817 


-61 


77.00 


281 .146 


281 .084 


-62 


77.38 


286.829 


286 . 766 


-63 


77.41 


287.182 


287.119 


-63 


77.71 


290.557 


290.494 


-63 


77.79 


291.817 


291.764 


-53 


78.00 


293 . 568 


293.516 


-52 


78.20 


296.398 


296 . 343 


-55 


78.39 


298.481 


298.426 


-55 


78.68 


301.810 


301.761 


-49 


78.70 


301.435 


301 .385 


-50 


79.12 


304.822 


304.777 


-45 


79.46 


307.954 


307.913 


-41 


79.62 


308.611 


308 . 570 


-41 


79.66 


308 . 593 


308 . 549 


-44 


80.11 


311.607 


311.564 


-43 


80.13 


311 .644 


311.603 


-41 


80 . 39 


314.415 


314.368 


-47 


80.43 


313.430 


313.382 


-48 


80.64 


315.296 


315.243 


-53 


81.02 


317.189 


317.135 


-54 


81.10 


317.522 


317.468 


-54 


81.27 


319.547 


319.490 


-57 


81.47 


320.843 


320.780 


-63 


81.54 


320 . 256 


320.195 


-61 


82.08 


321 .649 


321 .581 


-68 


82.38 


323.208 


323.139 


-69 


82.63 


324.023 


323.960 


-63 


82.81 


326.154 


326.090 


-64 


83.41 


328.882 


328.833 


-49 


83.55 


328.729 


328.680 


-49 


83.89 


331.510 


331.483 


-27 


84.15 


336 . 349 


336.325 


-24 


84.27 


334.223 


334.202 


-21 


84.56 


337.819 


337.848 


+29 


85.14 


350 . 094 


350.366 


+272 


85.20 


349.924 


350.184 


+260 


85.68 


354.753 


355.066 


+ 313 


85.88 


357.159 


357.518 


+359 


86.07 


358.225 


358.627 


+402 


86.50 


363.916 


364.438 


+522 


86.71 


366.635 


367.179 


+544 


86.92 


369.563 


370.132 


+569 


87.15 


372.438 


373.042 


+604 


87.18 


372.727 


373.334 


+607 


87.40 


376.163 


376.778 


+615 


87.62 


378.871 


379.470 


+599 


87.86 


382.361 


382.933 


+572 


88.09 


387.904 


388.451 


+547 


88.42 


385.649 


386.126 


+477 


88.98 


387.496 


387.672 


+ 176 


89.05 


388.097 


388 . 280 


+ 183 


89.31 


387.883 


388.103 


+ 220 


89.71 


386.787 


386.898 


+ 111 


89.93 


388.510 


388.652 


+ 142 


90.27 


390.562 


390.713 


+ 151 


90.41 


390.220 


390.393 


+ 173 



Sun Valley (continued) 



Pacoima. 



East of Van Norman 
Lake. 



08-25920(CofLA) 

V 786 = 08-25950 

08-25982(CofLA) 

08-2601 l(Cof LA) 

08-26070(CofLA) 

08-26040(CofLA) 

08-26060 = 34204 (LACo). . . 

P 43=08-26130 

08-26 160(Cof LA) 

Y 786 = 08-26190 

03-01685(CofLA) 

03-01687(CofLA) 

03-01710(CofLA) 

G 1142=03-01712 

03-01 755(Cof LA) 

03-01 770(CofLA) 

03-01800(CofLA) 

03-01830(CofLA) 

03-01860(CofLA) 

03-01890(GofLA) 

N 898=03-01930 

03-01950(CofLA) 

03-01980(CofLA) 

03-020 10(Cof LA) 

03-02040(CofLA) 

E 1142=03-02068 

03-02070(CofLA) 

03-02 100(Cof LA) 

03-02 125(CofLA) 

03-02 130(Gof LA) 

R 43 Reset 1955 = 03-02160. . 

03-02 190(Cof LA) 

03-02 195(CofLA) 

03-02220(CofLA) 

S 43 Reset 1966 = 03-02251 . . 

1066 (USGS) Reset 1966 = 03- 
02254. 

03-023 10(Cof LA) 

03-02340(CofLA) 

D 1142=03-02355 

03-02370(CofLA) 

03-02430(CofLA) 

03-02429(CofLA) 

03-02440(CofLA) 

03-02450(CofLA) 

03-06690(CofLA) 

03-02490(CofLA) 

03-02520(CofLA) 

P 53 Reset 1932 = 04-04590. . 

04-04620(CofLA) 

04-04635(CofLA) 

04-04650(CofLA) 

04-04680(CofLA) 

04-047 10(Cof LA) 

04-04720(CofLA) 

RS 10 (USGS) =04-04740. . . , 

04-04760(CofLA) 

04-04770(CofLA) 

04-0480 l(Cof LA) 

04-04830(CofLA) 

O 53 Reset 1950 = 04-04860. . 

04-04890(CofLA) 

04-00790(CofLA) 

04-00820(CofLA) 

04-00840(CofLA) 

04-00855(CofLA) 



15 



310 



San Fernando Earthquake "I 1971 



Table 1 —Line of level*, s«», Pedro to 1.9 l<ni math oj Grapevine— ■Continued 



Location 



I'.' m h mark 






ition 


Aj,j>. 










arthqualcc 




in 


a, 




396 449 




208 


•iio m 


410 549 




407 989 


408 050 




407 984 


408 083 




410 000 


419 707 


4-71 


440 027 


440.715 


+88 


452.417 


432.495 




438.977 


439 039 




543 991 


544 053 




036 


526 057 




502.873 


502.917 


+ 44 


486 866 


486.893 


-r27 


476.923 


470 941 




473.172 


47 V 20', 


+ 33 


lot 196 


404.422 




445 159 


445.378 


+19 


410.704 


430.780 




427.027 


427.640 


+ 13 


427 


427.04', 


+ 18 


42 i . 242 


423 258 


+16 


417.807 


417.825 


+18 


413.200 


413.270 


+ 16 


410.981 


410.995 


+ 14 


407.344 


407 


-20 


398 . 1 38 


398 . 1 38 





397.045 


397.053 


+8 


396.908 


396.921 


+ 13 


414.222 


414.237 


+15 


408.801 


408.863 


-2 


384 . 725 


384.746 


+21 


380.067 


380.084 


-17 


380.608 


380.624 


+ 16 


384.470 


384.499 


- 


383 . 654 


383.683 


-29 


370.799 


370.820 


+21 


363.290 


363.322 


+32 


357.049 


357.104 


+55 


309.104 


309.105 


+ 1 


310.803 


310.808 


+ 5 


316.432 


316.434 


+2 


319.517 


319.519 


+2 


324.841 


324.846 


-5 


328.892 


328.896 


+4 


332.823 


332.832 


+9 


342.453 


342.465 


+ 12 


350.991 


351.008 


+ 17 


354.987 


354.999 


+ 12 


375.040 


375.073 


+33 


419.758 


419.781 


+23 


440.883 


440.907 


+24 


467.049 


467.072 


+23 


486.979 


486.999 


+20 


498.556 


498.596 


+40 


502.436 


502.459 


+23 


571.015 


571.037 


+22 


582.958 


582.976 


+ 18 


618.456 


618.478 


+22 


656.817 


656.842 


+25 


671.895 


671.918 


+23 


702.363 


702 . 380 


+ 17 


726.924 


726.952 


+28 


742.635 


742.656 


+21 


774.591 


774.604 


+ 13 



East of Van Norman 
Lake (continued). 



Castaic Junction. 



Castaic. 



km 

04 00872(CofLA) 90 57 

04 00900(CofLA) 90 88 

04 00930=60 7(1. AC,,, 91.22 

C 1142=04 00935 -60-7 A(LACo). 91.27 

04-07660(CofLA) 91 .97 

04-07690 = 00 8A (LACo) 

Q 898 = 60-8 

M 53=60-9 93 01 

60-14A(CSDH) 94.45 

60-16(CSDH) 94 83 

60-19(CSDH) 95.27 

60-21(CSDII) 95 63 

60-22(CSDH) 95 86 

60-23(CSDH) 95.95 

60-23A(CSDH) 96. 15 

60-25A(LACo) 96.68 

60-27(CSDH) 97.27 

60-28(CSDII) 07 V, 

60-28A(LACo) 

60-29(CSDII) 97.93 

60-30(CSDH) 98.09 

60-29A(CSDH) 98.34 

60-30A(CSDH) 98.54 

60-31 A(CSDH) 99.16 

60-32(CSDH) 100.02 

60-32A(LACo) 100.04 

60-32BfLACo) 100.48 

60-32C(CSDH) 101.16 

60-33A(CSDH) 101.49 

60-34A(LACo) 102.03 

60-35A(LACo) 103.07 

60-35B(CofLA) 103. 12 

60-36 103.90 

49(CHC) = 60-38 105.17 

Q 370 = 60-39 106.25 

60-40(LACo) 107.06 

R 370 = 60^1 107.96 

U 370 114.09 

208-80(LACo) 114.93 

M 52 Reset 1967 = 205-12A 115.62 
(LACo). 

208-79(LACo) 1 16 . 55 

V 370 = 205-13 (LACo) 117.23 

208-78(LACo) 1 1 7 . 72 

W 370 Reset 1967 = 208-77(LACo). 118.49 

R 970 Reset 1967 =208-76(LACo). 119.25 

5 970 = 208-74(LACo) 120.76 

208-73(LACo) 121.39 

X 370 = 208-72(LACo) 122.14 

208-70(LACo) 123.10 

P 52 = 208-69(LACo) 123.52 

208-68(LACo) 124.04 

T 970 = 208-67(LACo) 124.81 

208-66(LACo) 125.24 

208-65(LACo) 125.86 

208-64(LACo) 126.90 

208-63(LACo) 127.42 

208-62(LACo) 128.03 

Z 370 Reset 1967 = 208-61 (LACo). 128.67 

208-60(LACo) 129.18 

208-59(LACo) 129.74 

M 450 = 208-58( LACo) 130.19 

208-57(LACo) 130.57 

208-56(LACo) 131.11 



17 



18 



Vertical Cruslal Movements 



311 



Table I.— Line of levels, San Pedro to 4.9 km north of Grapevine— Continued 



Location 



Bench mark 





Elevation 


Apparent 


Distance 






movement 








Preearthquake 


Postearthquake 




km 


m 


m 


mm 


131.66 


808 . 280 


808 . 302 


+22 


132.03 


828.989 


829.005 


+ 16 


132.59 


853.607 


853.622 


+ 15 


133.70 


889.138 


889.154 


+ 16 


135.68 


855.942 


855.962 


+20 


136.34 


893.276 


893.291 


+ 15 


137.57 


950 . 394 


950.407 


+ 13 


139.89 


952.272 


952.287 


+ 15 


140.65 


983.469 


983.487 


+ 18 


141.89 


1015.323 


1015.338 


+ 15 


143.13 


' 971.016 


971 .036 


+20 


143.58 


963.188 


963 . 202 


+ 14 


144.88 


967.858 


967.870 


+ 12 


145.60 


1011.035 


1011.049 


+ 14 


145.96 


1030.926 


1030.943 


+ 17 


146.74 


1071.010 


1071.026 


+ 16 


147.80 


1044.201 


1044.217 


+ 16 


148.29 


1071.753 


1071.768 


+ 15 


148.97 


1111.168 


1111 .183 


+ 15 


149.31 


1132.530 


1132.546 


+ 16 


150.21 


1183.520 


1183.536 


+ 16 


150.64 


1160.612 


1160.626 


+ 14 


151.27 


1130.159 


1130.173 


+ 14 


152.28 


1088.869 


1088.886 


+ 17 


152.92 


1068.463 


1068.474 


+ 11 


153.66 


1104.423 


1104.436 


+ 13 


153.69 


1104.727 


1104.737 


+ 10 


154.41 


1141.452 


1141.464 


+ 12 


154.74 


1158.917 


1158.931 


+ 14 


156.22 


1150.689 


1150.704 


+ 15 


156.36 


1146.653 


1146.667 


+ 14 


157.28 


1133.833 


1133.847 


+ 14 


157.72 


1124.605 


1124.620 


+ 15 


158.01 


1142.498 


1142.511 


+ 13 


158.57 


1150.130 


1150.143 


+ 13 


159.20 


1175.036 


1175.054 


+ 18 


159.68 


1201.161 


1201.178 


+ 17 


160.92 


1248.523 


1248.539 


+ 16 


161.04 


1255.670 


1255.687 


+ 17 


161.20 


1260.847 


1260.865 


+ 18 


161.96 


1283.785 


1283.803 


+ 18 


162.49 


1287.686 


1287.706 


+20 


163.33 


1281.029 


1281.045 


+ 16 


164.17 


1269.256 


1269.272 


+ 16 


164.93 


1222.341 


1222.360 


+ 19 


165.69 


1198.686 


1198.702 


+ 16 


165.90 


1187.817 


1187.835 


+ 18 


166.22 


1165.727 


1165.745 


+ 18 


166.57 


1148.907 


1148.926 


+ 19 


167.11 


1118.177 


1118.197 


+20 


167.59 


1095.417 


1095.439 


+22 


168.02 


1069.943 


1069.962 


+ 19 


168.37 


1052.095 


1052.117 


+ 22 


171.53 


1015.674 


1015.705 


+31 


171.55 


1016.080 


1016.110 


+30 


171.56 


1016.412 


1016.441 


+29 


172.09 


1016.563 


1016.596 


+ 33 


172.51 


1015.213 


1015.241 


+28 


172.56 


1014.648 


1014.678 


+30 


172.61 


1014.896 


1014.924 


+28 


172.66 


1014.852 


1014.877 


+25 



Castaic (continued). 



N 450 = 208-55(LACo) 

208-54(LACo) 

U 970 = 208-53(LACo) 

P 450 = 208-52(LACo) 

2807(USGS) = 208-50(LACo). . . 

T 52 = 208-49(LACo) 

W 12(DWR)=208-48(LACo)... 
R 450 = 208-47(LACo) 

V 970 = 208-45(LACo) 

W 970 = 208-44(LACo) 

N 370 = 208-43(LACo) 

L 992 = 208-42( LACo) 

M 3 70 = 208-41 (LACo) 

K 992 = 208-40(LACo) 

W 52 = 208-39(LACo) 

L 370 = 208-38(LACo) 

J 992=208-37(LACo) 

K 370 = 208-36(LACo) 

X 970 = 208-35(LACo) 

H 992 = 208-34(LACo) 

Q53 = 208-33(LACo) 

G 992 = 208-32(LACo) 

R 53= 208-3 l(LACo) 

J 370 = 208-30(LACo) 

F 992 =208-29(LACo) 

208-28A(LACo) 

S 53 = 208-28(LACo) 

B 992 = 208-27(LACo) 

H 370 = 208-26(LACo) 

G 370 = 208-24(LACo) 

Z 991 =208-23(LACo) 

Y 991 =208-22(LACo) 

T 53 = 208-2 l(LACo) 

X 991 =208-20(LACo) 

W 991 =208-19(LACo) 

Y 970 = 208-18(LACo) 

F 370 = 208-1 7(LACo) 

V 991 =208-16(LACo) 

T 991 =208-15(LACo) 

E 370 = 208-14(LACo) 

S991=208-13(LACo) 

V 53 = 208-1 2(LACo) 

R 991 =208-1 l(LACo) 

W 53 = 208-10(LACo) 

208-9(LACo) 

D 370 = 208-8(LACo) 

U 991=208-7(LACo) 

208-6(LACo) 

208-5(LACo) 

208-4(LACo) 

X53 = 208-3(LACo) 

208-2(LACo) 

208-l(LACo) 

Quail F RM 1 = 102-82B(LACo). 

Quail F = 102-82A(LACo) 

Quail F RM 2 = 102-82C (LACo) . 

Quail B=102-82D(LACo) 

Z 973 Reset 1965=102-83A 
(LACo). 

Y 973 Reset 1965 = 102-83B 
(LACo). 

X 973 Reset 1965=102-83C 

(LACo). 
W 973 Reset 1965=102-83D 

(LACo). 



20 



23 



312 San Fernando Earthquake of 1971 



Table I.— Line of levels, San Pedro to 1.9 km north u\ <.<n\,n kl£— Continued 



Location 



Bench mark 







App; 


Distant e 
















Pro arthi 


q iake 




km 


m 


m 


mm 


172.72 


1013 879 


1015 906 




172.82 


1010 543 


1010 




172.90 


1011 .208 


1011 240 




172.95 


1012 175 


1012 185 




173.00 


1013 080 


101 5 112 




173.05 


1014 055 


1014 080 


f3l 


173.10 


1014 002 


1014 004 




175.15 


101 882 


101 VOI 5 




173.20 


1010 701 


1010 70 5 




17', 55 


10 51 281 


1051 314 


4-33 


1 73 . 75 


10 50 158 


10 50 100 




174.04 


1040 986 


1050 017 


4-31 


1 74. 3 5 


1007 948 


1007 080 




174.8'* 


1002 8,08 


1092 




175.09 


1086.052 


1086.086 




175.62 


1001 494 


1001 529 


4-35 


I7i. .00 


1054.418 


1054.451 


+33 


176 i\ 


1061.383 


1001.419 




176.85 


1062 ',10 


1062.551 


+ 35 


177.32 


1070 8,0 5 


1070 028 


+ 35 


177. dO 


1080 398 


1080.434 


+ 36 


178.05 


1084.781 


1084.815 




178.55 


1097.446 


1097.479 




179.04 


1106.982 


1107.039 


+57 


179.23 


1111.551 


1 1 1 1 . 585 


+ 34 


179.78 


1127.100 


1127.132 


+32 


180.45 


1153.097 


1153.128 


+ 31 


180.99 


1101.640 


1101.674 


+ 34 


183.57 


1248.561 


1248.589 


+28 


184.20 


1274.429 


1274.468 


+ 39 


184.91 


1236.127 


1236.163 


+36 


186.39 


1196.150 


1196.188 


+38 


186.71 


1166.946 


1166.986 


+40 


186.73 


1166.631 


1166.671 


+40 


186.74 


1166.690 


1166.730 


+40 


187.14 


1141.144 


1141.184 


+40 


187.69 


1131.207 


1131.247 


+40 


189.07 


1097.731 


1097.772 


+41 


189.27 


1088.436 


1088.478 


+42 


189.44 


1089.642 


1089.684 


+42 


190.82 


1055.802 


1055.850 


+48 


192.49 


1020.122 


1020.168 


+46 


193.72 


997.474 


997.518 


+44 


193.90 


985.332 


985.381 


+49 


195.44 


954.026 


954.075 


+49 


196.81 


887.557 


887.605 


+48 


197.90 


827.922 


827.968 


+46 


198.23 


812.158 


812.209 


+ 51 


198.43 


800.158 


800.205 


+47 


198.97 


769.253 


769.303 


+50 


199.25 


752.847 


752.896 


+49 


199.67 


725.069 


725.117 


+48 


200.76 


661.638 


661.682 


+44 


201.25 


633.836 


633.882 


+46 


202.12 


580.055 


580.104 


+49 


202.77 


534 . 326 


534.371 


+45 


203.05 


524 . 548 


524.592 


+44 


203.50 


502.218 


502.262 


+44 


204.62 


457.186 


457.228 


+42 



Castaic (continued). 



Gorman . 



Lebec . 



V 973 Reset 1965=102 B3E 
(LACo). 

U 973 = 102 84A(LACo) 

S 973= 102 84B(LACo) 

R 973 = 102 H4C( LACo) 

Q973 = 102-84DH.ACo) 

P 973 = 102-84E( LACo) 

N 973 <=102-84F( LACo) 

M 973=l02-84K(LACo) 

Q 452 = 102-85(LACo) 

Z 53 Reset 1953 = 102 HO(LACo). 

P 452=102 87(LACo) 

N 452=102-88(LACo) 

102 88A(LACo) 

B 370=102 89( LACo) 

M 452= 102-90( LACo) 

L 452=102-91(LACo) 

A 370= 102-92( LACo) 

K 452 = 102-93(LACo) 

J 452 = 102-94( LACo) 

A 54 = 102-95(LACo) 

H 452 = 102-96(LACo) 

G 452 = 102-97( LACo) 

F 452 = 102-98(LACo) 

R 608= 102-99( LACo) 

E 452=102-100(LACo) 

102-100A(LACo) 

Z 368=102-101(LACo) 

B54 = 102-102(LACo) 

102-106(LACo) 

102-107(LACo) 

102-108(LACo) 

102-1 10(LACo) 

Boundary Monument 1 = 102-1 1 1 

(LACo). 
+00( L ACRD ) = 1 02- 1 1 2( LACo ) . 
Boundary Monument 2= 102-13 

(LACo). 

B 650= 102-1 14( LACo) 

H 971 = 102-1 15(LACo) 

E 54 

D 54 

P 1059 

F 54 

U 594 

T 1098 

G 54 

U 974 

V974 

J 537 Reset 1960 

S 1098 

E 367 

H 537 

D 367 

G537 

R 1098 

T974 

Z 365 

G 540 

Q 1098 

P 1098 

T824 Reset 1958 






25 



Vertical Crastal Movements 



313 



Table 2.— Line of levels, Monlalvo to 6.9 km south of Rosamond 



Location 



Bench mark 



Distance 


Elevation 


Apparent 
movement 












Preearthquake 


Postearthquake 






km 


m 


m 


mm 


mm 


0.00 


29.283 


29.255 


-28 


20 


0.68 


28.927 


28.910 


-17 


20 


1.76 


37.023 


37.010 


-13 




2.82 


44.199 


44.183 


-16 




2.84 


44.193 


44 . 1 76 


-17 




4.48 


50.722 


50.704 


-18 




5.33 


43.771 


43.752 


-19 




6.28 


38.964 


38.940 


-24 


20 


7.05 


43.668 


43.647 


-21 




7.57 


45.941 


45.928 


-13 




7.93 


48.630 


48.612 


-18 




9.01 


53.494 


53.477 


-17 




9.91 


57.379 


57 . 360 


-19 




10.79 


59 . 1 1 1 


59.095 


-16 




11 .80 


64.901 


64.883 


-18 




12.98 


64.232 


64.215 


-17 




13.62 


66.496 


66.478 


-18 




14.11 


68 . 349 


68.332 


-17 




14.82 


71.427 


71.409 


-18 




15.43 


68.893 


68.875 


-18 


20 


20.58 


95.350 


95.337 


-13 




21.66 


92.812 


92 . 796 


-It) 




22.58 


94.941 


94.928 


-13 




23.68 


103.358 


103.342 


-16 




24.35 


108.191 


108.177 


-14 




24.91 


113.025 


113.013 


-12 




25.69 


119.582 


119.573 


-9 




31.35 


153.622 


153.622 







31.53 


135.857 


135.854 


-3 




32.31 


136.284 


136.280 


-4 


19 


32.85 


136.752 


136.749 


-3 




32.96 


137.029 


137.026 


-3 




33.63 


132.618 


132.612 


-6 




34.71 


139.040 


139.032 


-8 




35.23 


143.056 


143.049 


-7 




35.65 


146.369 


146.362 


-7 




36.14 


145.685 


145.677 


-8 




37.00 


139.213 


139.205 


-8 




38.12 


142.681 


142.669 


-12 




38.54 


147.668 


147.656 


-12 




39.24 


152.116 


152.102 


-14 




40.29 


162.866 


162.853 


-13 




41 .40 


164.375 


164.355 


-20 


19 


42 . 22 


171.368 


1 7 1 . 348 


-20 




42.89 


177.763 


177.743 


-20 




43.65 


183.596 


183.570 


-26 




45.38 


190.349 


190.326 


-23 




46.26 


202 . 220 


202 . 200 


-20 




47.05 


206.664 


206.650 


-14 




47.47 


211.099 


211.088 


-11 




47.49 


210.678 


210.668 


-10 


18 


47.87 


213.750 


213.749 


-1 




48.58 


209.989 


209.980 


-9 




49.35 


209.530 


209.511 


-19 




50.29 


215.319 


215.306 


-13 




50.99 


220.554 


220.547 


-7 




51.34 


222.498 


222.496 


-2 




51.53 


225.709 


225.708 


-1 




52.51 


231.078 


231.087 


+9 




52.74 


231.683 


231.692 


+9 




53.44 


231.892 


231.900 


+8 


18 


54.15 


238.024 


238.028 


+4 




54.59 


236.808 


236.816 


+8 




55.05 


238.392 


238.401 


+9 




55.76 


245.701 


245.712 


+ 11 





Montalvo. 



Santa Paula. 



Fillmore. 



H 1051 

102-6 (VCo).... 
RV 2 (SPCo)... 

26 (CofV) 

RV 3 (SPCo). . . 

RV5 (SPCo). .. 
RV6 (SPCo)... 
102-7 (VCo).... 

V 304 

149(USGS) 

56-2 (CofV)... 
102-8 (CofV).. 
102-9 (CofV).. 

W 304 

RV9(SPCo). .. 

RV 10 (SPCo).. 

X 304 

102-10 (CofV). 
RV 12 (SPCo). . 
RV 13 (SPCo). . 

RV 19 (SPCo). . 

65-4 (VCo) 

RV 21 (SPCo). . 
102-13 (VCo)... 
RV22 (SPCo). . 

102-14 (VCo)... 
RV 23 (SPCo). . 

501 (USGS) 

5-67 (VCo) 

RV 28 (SPCo). . 

8-81 (VCo) 

RV 29 (SPCo). . 
19-203 (VCo)... 
RV 30 (SPCo). . 
E 305 

RV 32 (SPCo).. 
102-15 (VCo)... 
102-16 (VCo)... 
102-17 (VCo)... 
102-18 (VCo)... 

102-19 (VCo)... 
102-20 (VCo)... 
RV 35 (SPCo). . 
102-21 (VCo)... 
RV 37 (SPCo). . 

102-22 (VCo)... 
102-23 (VCo)... 
RV 40 (SPCo) . . 
102-24 (VCo)... 
H 305 

RV41 (SPCo).. 
102-25 (VCo)... 
RV43 (SPCo). . 
RV 44 (SPCo). . 
RV45 (SPCo). . 

RV 46 (SPCo).. 
SP 30 (VCo).... 

J 305 

RV47 (SPCo). . 
RV48 (SPCo). . 

RV49 (SPCo). . 
SP 33 (VCo).... 
RV 50 (SPCo). . 

K 305 

RV51 (SPCo). . 



3M San Fernando Earthquake <>\ 1971 



Table 2.— Line of levels, Montalvo to 6.9 km south of Hosarnond— Continued 



Location 



Bench mark 



at <- 


Elevation 


Apparent 










lV-'-artlj<juak<- 


I - -, " artbquake 




km 


m 


m 


mm 


56 80 


253 354 


253 361 




r >7 . 30 


2 r >4 481 


204 490 




r >8.41 


262 042 


262 056 


+ 14 


r ,;; 60 


201 .007 


261 020 


\ 19 


59 40 


2< ,3.900 


2', ', 914 


+ 14 


60.49 


273.465 


27 ', 500 


4-15 


61 .29 


27 ', 092 


273 103 


4-11 


62.14 


281 014 


281 .625 


4-11 


(.2 . 52 


288.173 


288 187 


+ 14 


63.05 


288 . 1 79 


288 192 


\ 13 


63.71 


287 526 


287.535 


+9 


64.05 


288 . 89 ', 


288 897 


~4 


65.24 


297 . 596 


297 GO 1 


+ 7 


66.33 


303.305 


303.309 


4-4 


1,7.33 


307 . 896 


307 901 


+ 5 


67.40 


307.114 


307 .112 


-2 


(,7.83 


104 


309.105 


+ 1 


68 . 76 


314.052 


314.062 


+10 


69.20 


317.464 


317.485 


+21 


70.12 


325.542 


325.572 


+30 


70.24 


327.817 


327.80 3 


+46 


70.42 


327.840 


327.888 


+ 48 


70.93 


329.558 


329.605 


+ 47 


71.72 


335.143 


335.194 


+51 


71 .73 


335 . 348 


335.400 




72.77 


342.609 


342.00 3 


+ 54 


73.24 


345.843 


345.907 


+64 


74.12 


350 . 530 


350.591 


+61 


74.61 


353.820 


353.880 


+60 


75.15 


356.572 


356.589 


-17 


75.25 


351.772 


351.834 


+62 


75.31 


352.187 


352.245 


+58 


76.02 


357.481 


357.535 


+54 


77.00 


363 . 957 


364.014 


+ 57 


78.97 


377.630 


377.705 


+75 


80.01 


388.741 


388 . 784 


+43 


80.78 


396.995 


397.063 


+68 


81.71 


409 . 509 


409 . 588 


+ 79 


82.24 


416.320 


416.422 


+ 102 


82.62 


416.035 


416.119 


+84 


83.54 


426.794 


426.935 


+ 141 


84.34 


438.802 


438.941 


+ 139 


122.09 


968 . 759 


968.805 


+46 


122.10 


968.815 


968.863 


+48 


122.15 


970.517 


970.564 


+47 


122.20 


970.707 


970.756 


+49 


122.44 


975.192 


975.238 


+46 


122.69 


983.048 


983.093 


+45 


122.85 


982.838 


982.883 


+45 


123.02 


983.269 


983.316 


+47 


123.18 


981.399 


981.445 


+46 


123.27 


983.541 


983.587 


+46 


123.65 


977.125 


977.175 


+50 


123.85 


976 . 345 


976.387 


+42 


124.10 


978.986 


979.029 


+43 


124.27 


979.973 


980.019 


+46 


124.36 


979.765 


979.809 


+44 


124.49 


975.887 


975.932 


+45 


124.71 


965 . 562 


965.607 


+45 


1 24 . 90 


955 . 225 


955.267 


+42 


125.15 


942.836 


942.876 


+40 


125.16 


942.973 


943.013 


+40 


125.23 


940 . 365 


940.406 


+41 


125.37 


935.064 


935.105 


+41 


125.45 


932.334 


932.374 


+40 



Piru (continued). 



Castaic Junction. 



Saugus. 



RV 52 (SPCo) 

KV 53 (SPCo) 1909 Kiev 

C 41 

RV 55 (SPCo) 

206-33 (LACo) 

206-21 (LACo) 

RV 57 (SPRR) = 206-22 (LACo). . . 

206 24A (LACo) 

200-24 (LACo) 

RV 58 (SPRR) = 206-25 (LACo). . . 

RV 59 (SPRR) = 206-26 (LACo). . . 

206-27 (LACo) 

206-29 (LACo) 

206-30 (LACo) 

206-31 (LACo) 

RV 60 (SPRR) = 206-31 A (LACo). . 

U 370 = 206-32 (LACo) 

RV 62 (SPRR) = 208-81 (LACo). . . . 

208-82 (LACo) 

RV 64 (SPRR) = 208-83 (LACo). . . . 
Q 970 = 208-84 

RV 65 (SPRR) = 208-85 (LACo). . . . 

T 370 = 208-86 (LACo) 

208-87 (LACo) 

208-87A (LACo) 

S 370 Reset 1964 = 208-88 (LACo). . 

208-89 (LACo) 

208-90 (LACo) = RV 68 (SPRR). . . . 

J 52 = 208-91 (LACo) 

1171 (USGS) =60-42 (LACo) 

C 1148=60-43A (LACo) 

X 898 = 60^3 (LACo) 

201-121A (LACo) 

201-120 (LACo) 

Y 984 = 201-1 18A (LACo) 

201-1 16A (LACo) 

201-1 15A (LACo) 

201-114 (LACo) 

201-113 (LACo) 

201-112 (LACo) 

201-1 1 1A (LACo) 

201-1 10A (LACo) 

BM (SCE) = 201-65 (LACo) 

SEC 22-27 (LACS) = 201-64 
(LACo). 

Sloot = 201-63 (LACo) 

W 31 Reset 1955 = 201-62 (LACo).. . 

V 431 =201-61 (LACo) 

U 431 =201-60 (LACo) 

Mont 2 = 201-59 (LACo) 

F 1000 = 201-58 (LACo) 

3219 (USGS) =201-57 (LACo) 

S 431 =201-56 (LACo) 

Q 431 =201-54 (LACo) 

H 57 = 201-53 (LACo) 

Q 81 1=201-52 (LACo) 

L 899 = 201-51 (LACo) 

A 994 = 201-50A (LACo) 

M431 Reset 1963 = 20 1-49A (LACo). 

E 1000 = 201-48 (LACo) 

K 431=201-47 (LACo) 

Atlas = 201-45 (LACo) 

Atlas RM = 201-44 (LACo) 

M 899 = 201-43 (LACo) 

N 899 = 201-42 (LACo) 

P 899 = 201-41 (LACo) 



18 



18 



18 



18 



18 



21 



Vertical Crustal Movements 



315 



Table 2.— Line of lei'els, Montalvo to 6.9 km south of Rosamond— Continued 



Location 



Bench mark 



Distance 


Elevation 


Apparent 
movement 








Preearthquake 


Postearthquake 




km 


m 


m 


mm 


125.52 


937.253 


937.293 


+40 


125.65 


929.278 


929.317 


+ 39 


125.77 


924.514 


924.554 


+40 


126.05 


918.042 


918.082 


+40 


126.14 


914.738 


914.777 


+39 


126.32 


908.099 


908.137 


+38 


126.61 


902.612 


902.650 


+38 


126.69 


900 . 706 


900 . 745 


+ 39 


126.77 


898.775 


898.815 


+40 


126.85 


896.458 


896.498 


+40 


126.92 


894.255 


894.299 


+44 


126.99 


892 . 396 


892.434 


+38 


127.13 


889 . 369 


889.415 


+46 


127.22 


887.418 


887.458 


+40 


127.39 


885.585 


885.623 


+ 38 


127.46 


884.929 


884.968 


+39 


127.54 


883.172 


883.210 


+ 38 


127.68 


880.970 


881 .008 


+ 38 


127.73 


879.983 


880.020 


+ 37 


127.81 


878.803 


878.842 


+ 39 


127.89 


877.799 


877.837 


+ 38 


127.97 


876.234 


876.273 


+ 39 


128.05 


875.293 


875.329 


+36 


128.21 


874.114 


874.152 


+ 38 


128.29 


872 . 709 


872.747 


+ 38 


128.45 


871 .641 


871.677 


+ 36 


128.51 


870.209 


870.245 


+36 


128.58 


869.470 


869.507 


+37 


128.63 


868.424 


868.464 


+40 


128.65 


867 . 743 


867.781 


+38 


128.69 


866.521 


866.561 


+40 


128.74 


865.908 


865.945 


+ 37 


128.79 


865.603 


865.644 


+41 


128.84 


864.798 


864.832 


+ 34 


128.89 


864.085 


864.118 


+ 33 


128.94 


863.493 


863.529 


+36 


128.99 


862.852 


862.885 


+33 


129.04 


862.410 


862.440 


+30 


129.09 


861.668 


861.704 


+36 


129.19 


863.155 


863.191 


+36 


129.24 


862.205 


862 . 238 


+33 


129.31 


862.847 


862.885 


+ 38 


129.40 


860.889 


860.924 


+35 


129.45 


860 . 706 


860.742 


+36 


129.54 


860.475 


860.510 


+35 


129.59 


859.707 


859.742 


+35 


129.64 


859.491 


859.526 


+35 


129.69 


858 . 595 


858.632 


+37 


129.74 


857.993 


858.024 


+31 


129.79 


857.208 


857.243 


+35 


129.84 


856.193 


856.231 


+38 


129.89 


855.753 


855.793 


+40 


129.94 


855.227 


855.265 


+ 38 


130.10 


853.788 


853.829 


+41 


130.17 


854.380 


854.415 


+35 


130.20 


854.479 


854.525 


+46 


130.24 


855.371 


855.410 


+ 39 


130.29 


854.887 


854.923 


+ 36 


130.32 


854.832 


854.867 


+35 


130.35 


854.866 


854.904 


+ 38 


130.37 


854.907 


854.961 


+54 


130.42 


854.839 


854.877 


+38 


130.58 


858.046 


858.081 


+35 


130.63 


856 . 760 


856.795 


+ 35 


130.68 


853.451 


853.486 


+35 



Saugus (continued). 



Loft A = 20 1-40 (LACo) 

Q 899 = 201-39 (LACo) 

R 899 = 201-38 (LACo) 

S 899 = 201-37 (LACo) 

P811 Reset 1955 = 201-36 (LACo). 
T 899 = 201-35 (LACo) 

Y 899 = 201-32 

W 899 = 201-31 

Z 899 = 201-30 

Y 899 = 201-29 

X 899 = 201-28 

DD 487 = 201-27 

T 430 = 201-25 

M 811 Reset 1955 = 201-24 

EE 487 = 201-22 

P 430 = 201-21 

N 430 = 201-20 

G 57 = 201-18 

L 430 Reset 1955 = 201-17 

K 430 = 201-16 

J 430 = 201-15 

H 430 = 201-14 

G430 = 201-13 

E 430 = 201-11 

D 430 = 201-10 

B 430 = 201-8 

D 1000 = 201-7 

Z 429 = 201-6 

109 (USFS) = 201-5 

Y 429 = 201-4 

X 429 = 201-3 

W 429 = 201-2 

Y 429 = 201-1 

U 429 = 101-1 

T 429= 101-2 

S 429 = 101-3 

R 429=101-4 

Q429=101-5 

P 429 =101-6 

M 429= 101-8 

L 429= 101-9 

Alpine =101-11 

J 429 = 101-12 

H 429=101-13 

F 429=101-15 

E 429= 101-16 

D 429 = 101-17 

C429=101-18 

B 429=101-19 

A 429=101-20 

Z 428=101-21 

Y 428 = 101-22 

X 428= 101-23 

U 428=101-26 

T 487 = 101-28 

Y 487 = 101-29 

S 428 = 101-30 

X 487 = 101-32 

Y 487 = 101-33 

Z 487 = 101-34 

Q 428 = 101-35 

P 428= 101-36 

Voir 2 = 101-39 

J 811 = 101-41 

H 811 = 101-42 



22 



22 



22 



310 



San Fernando Earthquake of 1971 



Table 2.— Line of levels, Hontalvo to 6.9 km south of BosamomU-4. onthmed 



Location 



Saugus (continued) , 



Bench mark 



Palmdale. 



I )L tan< • 



itiofl 



Preearthquake quake 



/ "i m ui 

A 4»H= 101 44 130.76 850.217 850.244 

B488-101-45 1 50 70 849.189 849.220 

C 488-101-46 130.82 848 848.453 

D 488-101 17 130.85 847.986 848.016 

C 1000-101-48A 130.88 847.603 847.633 

F428-101-48B 130.90 847.310 847 139 

F488-101-49 130.91 847.396 847.426 

G 488 = 101 50 130.93 846 635 

G 811-101-51 130 846 109 846 ',40 

D 428 Reset 1947=101-52 15100 845.818 845.849 

C428-101-53 131.05 844.142 844.173 

B 428 =101-54 131 .09 84 1 942 84 ', 973 

A 428 Reset 1004 = 101 55A 131 .14 842 302 842 . 1 1 1 

Y 427 = 101-57 131.25 8 50 839.309 

X427-101-58 131.28 837.762 857 701 

W 427=101-59 131.33 8 57.241 837.269 

V427-101-60 131.38 836.695 836.725 

J 488= 101-61 151.44 836.326 836.356 

11488 = 101-02 131.49 835.162 85', 102 

S 427 = 101-63 131.53 833.376 8 5 5.400 

R 427 = 101-04 151.58 83:3.449 855.479 

L 1 147 = 101-64A 131.59 833.5 50 83 5 

Q427 = 101-65 131 852.955 832.985 

P 427 = 101-66 131.69 851 775 851 802 

M427 = 101-68 151.79 820 829.718 

L 427= 101-69 131.84 829.047 829.077 

K 427 = 101-70 1.51.89 828.292 828.320 

J 427 = 101-71 131.97 827 071 827 000 

H427 = 101-72 132.04 820.339 826.369 

F427 = 101-74 132.20 822.516 822.545 

E427 = 101-76 132.28 821.884 821.911 

A 427= 101-80 132.60 816.603 816.027 

Y426=101-82 132.71, 815.728 815.750 

X426=118-l 132.84 814.408 814.450 

S 487 = 101-86 133.15 812.395 812.412 

R487 = 101-87 133.24 812.320 812.340 

0.487 = 101-88 133.35 812.225 812.246 

R426 = 101-89A 133.43 811.351 811 .572 

G 81 1 = 101-89 133.44 811.516 811.538 

Q426=101-91 133.52 811.338 811.358 

2657 (USGS) = 101-93 133.71 810.483 810.503 

X811 = 101-94 133.82 809.928 809.949 

B 81 1 = 101-95 133.85 810.333 810.352 

A 81 1 = 101-96 133.98 809.248 809.264 

M426=101-97 134.11 808.192 808.211 

L 426 = 101-98 134.23 808.113 808.133 

K 426= 101-99 134.36 806.300 806.320 

Palmdale 2 = 1 18-3A 134.63 805.272 805.296 

G 426 = 101-101 134.75 803.698 803.720 

F 426= 101-102 134.88 802.691 802.713 

E 426= 101-103 135.01 801.374 801.396 

D 426 = 101-104 135.13 800.253 800.276 

B 426 = 101-106 135.45 797.918 797.940 

P 487 = 101-107 135.71 797.702 797.722 

Z 425=101-108 135.83 796.760 796.779 

Y 425 = 101-109 136.02 797.263 797.282 

X425-101-110 136.20 797.525 797.543 

W 425 = 101-111 136.38 796.710 796.728 

A 1000= 101-112A 136.59 797.308 797.326 

V425 = 101-113 136.77 796.049 796.065 

U425=101-114 137.03 795.016 795.031 

T 425= 101-115 137.29 795.396 795.413 

S 425=101-116 137.55 794.001 794.018 

Sahara = 101-1 17 137.64 794.452 794.469 

Sahara RM 4= 101-1 17A 137.66 794.569 794.586 

Sahara RM 3 = 101-1 17B 137.69 794.202 794.219 



Apparent 

meat 



i 51 

-51 

I 51 
J 51 

-28 
- 50 
4-30 

-50 

+30 

+ 30 
+ 29 

+ 30 

+28 
+28 
+30 

-29 
+27 

+24 
+22 
+22 
-17 
+20 

+21 
+21 
+22 
+20 
+20 

+21 
+ 19 
+ 16 
+ 19 
+20 

+20 

+24 
+22 
+22 
+22 

+23 
+22 
+20 
+ 19 
+ 19 

+ 18 
+ 18 
+ 18 
+ 16 
+ 15 

+ 17 
+ 17 
+ 17 
+ 17 
+ 17 



22 



22 



22 



22 



22 



Vertical Crustal Movements 



317 



Table 2.— Line of levels, Montalvo to 6.9 km south oj Rosamond— Continued 



Location 



Bench mark 





Elevation 


Apparent 


Distance 






movement 








Preearthquake 


Postearthquake 




km 


m 


m 


mm 


138.44 


789.637 


789.647 


+ 10 


139.13 


785.510 


785.520 


+ 10 


139.92 


779.054 


779.063 


+9 


140.70 


775.295 


775.302 


+ 7 


142.38 


761.407 


761.404 


-3 


142.66 


757.988 


757.986 


-2 


143.45 


751.049 


751.043 


-6 


143.92 


746.052 


746.042 


-10 


144.66 


738.643 


738.623 


-20 


145.49 


730.823 


730.786 


-37 


146.34 


725.274 


725.172 


-102 


147.02 


719.709 


719.579 


-130 


147.25 


717.088 


716.942 


-146 


148.02 


712.738 


712.603 


-135 


148.11 


712.393 


712.259 


-134 


148.37 


711.212 


711.083 


-129 


149.19 


709.910 


709.776 


-134 


149.70 


708.810 


708 . 708 


-102 


150.81 


706.496 


706.395 


-101 


151.39 


705.519 


705.424 


-95 


152.55 


702.824 


702.725 


-99 


153.27 


701.844 


701.753 


-91 


153.74 


701.687 


701.599 


-88 


153.75 


702.494 


702.406 


-88 


153.77 


701.652 


701.560 


-92 


154.74 


701.456 


701.363 


-93 


155.42 


700.870 


700.781 


-89 


156.28 


701.289 


701.208 


-81 


157.28 


701.557 


701.458 


-99 


158.04 


702.369 


702.286 


-83 


159.20 


702 . 393 


702.323 


-70 


159.67 


702.895 


702.841 


-54 


161.22 


703.542 


703.504 


-38 



Palmdale (continued). 



Rosamond . 



101-118 (LACo) 

W 811=101-119 

K 1147 = 101-120A 

V 81 1 = 101-121 

U 811 = 101-123 

B 57 Reset 1955=101-124. . 
2462 (USGS) = 101-124A... 

T 811 = 101-125 

101-126 (LACo) 

S811 Reset 1955=101-127. 

101-128 (LACo) 

G 487 = 101-130 

2356 (USGS) = 101-131A... 

101-132 (LACo) 

J 1147= 101-132A 

2335 (USGS) = 101-133 

Z 56 Reset 1965 = 101-134A. 

101-135 (LACo) 

Z 811 = 101-136 

101-137 (LACo) 

Y 56=101-138 

2302 (USGS)= 101-139 

Oban RM 1 = 101-140 

Oban (USGS)= 101-141. . . 
Oban RM 2=101-142 

H 487 = 101-143 

101-144 (LACo) 

T 1146=101-145A 

101-146 (LACo) 

J 487 = 101-147 

W 56=101-148 

N 487 = 101-149 

M 487 = 101-151 



23 



23 



318 San Fernando Earthquake of I'Jll 

Table J.— Line oj levels, 0.4 km west of Itrid^e So. 57-JJ wet Tofiiittgtt (reek to intenettion »j loot/ull lit, 'I and <> /. 

1. n (.inuutu 



Location 



Bench mark 



1 ). i.mcc 


I.I' . 


Appa 










<7 




Pr< • arthquake 


Po " -irtl, quake 






km 


rn 


m 


mm 




00 


8 774 


8 704 


-10 




(j 3 1 


11 .950 


11 ,940 


-10 




1 30 


24 . 544 


24.519 


-T> 




2.00 


159 


35 149 


-10 




2.35 


46 811 


4*. 802 


-9 




2.97 


07 . 520 


67.511 


-9 




3 . 78 


90.425 


90 410 


-10 




4.17 


99 618 


99 009 


-9 




1 54 


1 J2 831 


1 32 , 822 


-9 




4.92 


163.759 


163 7 72 


-7 




5.14 


180 811 


180 800 


-5 




5 7* 


208 . 297 


208 29 J 


-4 




0.07 


224.501 


224.490 


-11 




0.74 


223.981 


223.977 


-4 




7.41 


225.615 


225.010 


— 5 




8.01 


2 54 804 


234.858 


-6 




8.91 


246.033 


240.0 51 


-2 




9 . 52 


255.210 


255.211 


+ 1 




9.81 


21,1 .542 


201 .546 


+4 




10.63 


272.209 


272.209 







11.02 


277.478 


277.480 


+2 




11.35 


285.835 


285.833 


-2 




12.00 


$06,951 


306.957 


+6 




12.72 


327.352 


327.379 


-27 




12.76 


329.189 


329.181 


-8 




13.02 


341.898 


341.900 


+2 




13.33 


358.502 


358.502 







13.80 


388.601 


388.5% 


-5 




13.94 


388.180 


388.186 


+6 




14.94 


407.106 


407.108 


+2 




15.61 


433.167 


433.159 


-8 




15.95 


451 .449 


451.455 


+6 




16.14 


457.140 


457.143 


+3 




16.61 


439 . 583 


439 . 586 


+3 




17.21 


411.827 


411.826 


-1 




17.60 


394.338 


394.337 


-1 




17.85 


381.353 


381.349 


-4 




18.24 


358.662 


358.659 


-3 




18.59 


342.628 


342.625 


-3 




18.62 


341.196 


341.192 


-4 




18.83 


329.759 


329.759 







19.41 


301.970 


301.964 


-6 




19.96 


291.088 


291.085 


-3 




20.58 


280.534 


280.523 


-11 




21.04 


275.588 


275.580 


-8 




21.26 


271.878 


271.869 


-9 


16 


21.32 


268.409 


268.402 


-7 




21.39 


269.747 


269.737 


-10 




21.65 


266.641 


266.633 


-8 




21.67 


266.425 


266.418 


-7 




22.00 


262 . 792 


262.787 


-5 




22.21 


260.047 


260.043 


-4 




22.45 


256.572 


256 . 566 


-6 




22.68 


252.701 


252.695 


-6 




22.91 


249.747 


249 . 734 


-13 




23.31 


246.219 


246.213 


-6 




23.71 


244.190 


244.183 


-7 




23.84 


244.125 


244.117 


-8 




24.33 


242.237 


242.228 


-9 




24.56 


241.742 


241.736 


-6 




24.98 


243.340 


243.336 


-4 




25.21 


244.160 


244.155 


-5 




25.44 


245.023 


245.017 


— 6 




25.49 


244.837 


244.832 


— D 




25.70 


246.269 


246.264 


— o 





Santa Monica. 



Woodland Hills . 



I- ')') K.-srt 1933=48 02 . 

56-1A (LACo) 

56-1 (LACo) 

56 IB (LACo) 

56-2 (LACo) 

17-F3 (LACFCD) = 56 i 
53-143 (LACFCD)=56-4. 

56-4B (LACo) 

56-4C (LACo) 

56-4D (LACo) 

56-5 (LACo) 

56-5A (LACo) 

56-6 (LACo) 

RS 20A (USGS) = 56-7. . . 
A 50 = 56-8 

56-9 (LACo) 

56-10 (LACo) 

56-10A(LACo) 

56-10B (LACo) 

56-11 A (LACo) 

X 1135 = 56-11B 

56-12 (LACo) 

56-12A(LACo) 

56-13A(LACo) 

56-13 (LACo) 

A 10(LACE) = 56-13B... . 

56-13C (LACo) 

56-14 (LACo) 

X49 = 56-14A 

56-15 (LACo) 

56-15A(LACo) 

B 1 141 =56-15B 

56-16 (LACo) 

A 1141=56-17A 

56-17B (LACo) 

56-17C(LACo) 

56-18A (LACo) 

56-18B (LACo) 

56-19 (LACo) 

56-19A (LACo) 

56-19B 

56-20A(LACo) 

Y 1135 = 56-21A 

56-22 (LACo) =06-02280. 
T 1135 = 56-22A 

56-23 (LACo) =06-02400. 
57-35 (LACo) =06-06330. 

06-02405 (CofLA) 

06-02500 (CofLA) 

06-02520 (CofLA) 

06-02530 (CofLA) 

06-02560 (CofLA) 

06-02570 (CofLA) 

06-02590 (CofLA) 

06-02610 (CofLA) 

06-02640 (CofLA) 

06-02700 (CofLA) 

06-02732 (CofLA) 

06-02852 (CofLA) 

06-02910 (CofLA) 

06-02970 (CofLA) 

06-03005 (CofLA) 

06-03035 (CofLA) 

06-03060 (CofLA) 

06-03095 (CofLA) 



Vertical Crust al Movements 



319 



Table 3.— Line of levels, 0.4 km west of Bridge No. 53-35 over Topanga Creek to intersection of Foothill Blvd. and Ocean View Blvd., 

La Canada— Continued 



Location 



Bench mark 





Elevation 


Apparent 


Distance 






movement 








Preearthquake 


Postearthquake 




km 


m 


m 


mm 


25.92 


247.807 


247.802 


-5 


26.34 


250.551 


250 . 548 


-3 


26.74 


252 . 294 


252.291 


-3 


26.77 


252.480 


252.477 


-3 


27.01 


253.280 


253.275 


-5 


27.23 


254.586 


254.582 


-4 


27.38 


255.539 


255.536 


-3 


27.75 


258.282 


258.279 


-3 


27.96 


260.337 


260 . 338 


+ 1 


28.23 


263.624 


263.626 


+2 


28.45 


266.278 


266.278 





28.66 


268.455 


268.453 


-2 


28.81 


270.996 


270.993 


-3 


28.95 


271.045 


271.043 


-2 


29.15 


271.927 


271.921 


-6 


29.36 


272.158 


272.157 


-1 


29.47 


273.855 


273.855 





29.74 


276.036 


276.036 





29.90 


276.952 


276.951 


-1 


30.04 


275.817 


275.818 


+ 1 


30.11 


275.933 


275.930 


-3 


30.52 


289.561 


289.554 


-7 


30.78 


284.950 


284.953 


+ 3 


30.82 


283.095 


283.097 


+ 2 


30.83 


283.926 


283.927 


+ 1 


31.10 


284.547 


284.550 


+ 3 


31.54 


289.983 


289.988 


+5 


31.71 


291.227 


291.231 


+4 


31.97 


293.850 


293.850 





32.03 


292.719 


292.721 


+2 


32.24 


294 . 704 


294.706 


+2 


32.38 


295.959 


295.962 


+ 3 


32.69 


297.701 


297.705 


+4 


32.91 


297.829 


297.832 


+ 3 


33.32 


296.420 


296.422 


+2 


33.54 


293.314 


293.311 


-3 


33.78 


290.686 


290.689 


+3 


34.01 


291.516 


291.519 


+3 


34.20 


289.269 


289.272 


+3 


34.23 


289.092 


289.093 


+ 1 


34.63 


291.398 


291.401 


+ 3 


34.95 


290.648 


290.651 


+ 3 


35.08 


290.917 


290.919 


4-2 


35.47 


289.641 


289.645 


+4 


35.85 


293.138 


293.143 


+5 


36.32 


294 . 759 


294.764 


+5 


36.70 


295.868 


295.871 


+ 3 


37.12 


287.963 


287.964 


+ 1 


37.43 


285.227 


285.220 


-7 


37.56 


286.977 


286.974 


-3 


37.98 


293.831 


293.832 


+ 1 


38.53 


300.840 


300.836 


-4 


38.82 


299.093 


299.086 


-7 


39.05 


302.691 


302.687 


-4 


39.23 


299.256 


299.250 


-6 


39.66 


298.064 


298.060 


-4 


39.85 


298.073 


298.066 


-7 


40.58 


296.599 


296 . 598 


-1 


40.76 


294.569 


294.566 


-3 


40.99 


292.493 


292.492 


-1 


41.18 


290.861 


290.859 


-2 


41.21 


290.996 


290.994 


-2 


41.60 


289.124 


289.122 


-2 


41.78 


288.100 


288.098 


-2 


42.01 


285.213 


285.208 


-5 



Woodland Hills 
(continued). 



Granada Hills. 



06-03 1 50 
06-03180 
06-03210 
06-03242 
06-03272 

06-03300 
06-03332 
06-03362 
06-03388 
06-03422 

06-03450 
06-03483 
06-03485 
06-03510 
06-03541 

06-03600 
06-03610 
06-03620 
06-03655 
06-03690 

06-03720 
06-03760 
06-03770 
06-03840 
06-03839 

05-00420 
05-00450 
05-00475 
RS 17=05 
05-00540 

05-00830 
05-00825 
0.31=05 
05-00360 
05-00781 

05-00770 
05-00060 
05-00760 
05-00740 
05-00730 

04-02910 
04-02810 
04-02787 
04-02760 
04-02700 

04-01860 
04-02640 
04-02580 
04-02549 
04-02542 

04-02520 
04-02490 
04-01800 
04-02460 
04-02445 

04-02430 
04-02399 
04-02340 
04-02321 
04-02315 

04-02310 
04-02309 
94-02302 
04-01180 
04-01171 



CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
00535.. 
CofLA). 



CofLA). 
CofLA). 
00330. . . 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 



16 



320 



San Fernando Earthquake <>j 1971 



Table "l.—Line of levels, 0.4 km west oj Bridge A'o. 5 7—75 m>er Topanga Creek to tnUnection <>j looihiil in. 'i and Ocean \ • u-u Hlvd. 

l. n Canada —Continued 



Location 



Ui-n< h mark 



I I tance 



;tion 



Pr< ■ arthquakc Portearthquake 



Apparent 

I Mi<-nt 



Granada I Mils 

(continued). 



Olive View . 



Hansen Lake. 



04 01205 

04 01261 

04 01270 

04 01290 

04 01322 

04-05468 
04-04120 
04-05490 
04-05510 
04-05520 

04-04438 
04-04440 
04-05550 

04-0. r > r )7O 
04-05590 

04-05610 
04-051)12 
04-05660 
04-05662 

04-05690 

04-05720 
04-05761 
04-06200 
04-07400 
04-07410 

04-07425 
04-07455 
04-07465 
04-07475 
04-07485 

04-07495 
04-00872 
04-04950 
03-00995 

03-00990 
03-00962 
03-00930 

03-00900 
03-00850 
03-00840 
03-00820 
03-00810 

03-00780 
03-00771 
03-00770 
03-00751 
03-00750 

03-00720 
03-00670 
03-00657 
03-00631 
03-00630 

03-00620 
03-00607 
03-00547 
03-00542 
03-00540 

03-05010 
03-00480 
03-00421 
03-00391 
03-00360 
03-00330 



Col I, A) 

CofLA). 

Oof I. A) 
CofLA). 
CofLA). 

CofLA) 
CofLA). 
CofLA) 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA) 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
Cofl -A ) . 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 



CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 



f,w 

42.25 

42.47 
42 . 50 
42.65 

42.92 

43.01 

43.78 
43.82 

44.28 
44.51 

44.65 
44 . 70 
44.90 
45.14 
45.28 

45.63 
45.67 
46.30 
46.34 
46.74 

47.06 
47.56 
47.6b 
47.95 
48.12 

48.31 
48 . 75 
49.05 
49.22 
49.43 

49.54 
49.83 
53.96 
55.94 

56.39 
56.84 
57.29 

57.74 
57.96 
58.19 
58.74 
58.97 

58.99 
59.01 
59.03 
59.44 
59.85 

60.10 
60.19 
60.69 
61.16 
61.20 

61.50 
61.67 
61.89 
62.13 
62.22 

62.59 
63.04 
63.49 
63.73 
63.85 
64.28 



m 
284 788 
287.673 
287.843 

288 880 
290 645 

291 .416 
$00 865 
301 .2 52 
509 814 
315 24 5 

318.559 

3 1 9 . 287 
323.917 

528.919 
3 12 . 508 

341.497 
342 . 58 ', 
361 .079 
363.144 
376.693 

388.018 
397.111 
393.935 
386.357 
388.565 

392.391 
406 . 705 
420.038 
420.989 
414.162 

409.994 
396.449 
426.368 
420.725 

414.448 
407.008 
399.321 

394.783 
394.758 
393.248 
379.485 
378.803 

378.991 
369.895 
370.556 
363 . 763 
363.817 

363.155 
363.616 
357.541 
352.248 
352.002 

348.842 
350.781 
354.269 
353.731 
354.790 

352.752 
348.146 
339.057 
333.337 
329.477 
327.590 



III 


284 


782 


287 


664 


287 


8 57 


288 


872 


290 


.640 


291 


.411 


300 


«<, 2 


301 


251 


309 


812 


315 


24 5 


318 


. 562 


319 


290 


323 


91 5 


328 


.921 


332 


.513 


341 


. r ; 54 


342 


.624 


361 


681 


363 


.249 


376 


.802 


388 


112 


397 


248 


384.055 


386 


320 


388 


.579 


392 


380 


406 


822 


420 


124 


421 


185 


414 


395 


410 


137 


396 


657 


426 


838 


421 


285 


415 


093 


407 


776 


400 


310 


396 


027 


396 


040 


394 


573 


380.879 


380.255 


380 


451 


371 


314 


372 


066 


364 


037 


364 


072 


363 


356 


363 


760 


357 


618 


352 


311 


352 


070 


349.022 


350 


882 


354 


204 


353. 


649 


354. 


722 


352. 


685 


348. 


082 


338. 


992 


333. 


282 


329. 


423 


327. 


535 



iiiiii 

-6 
-9 

-6 
-8 
-5 

-5 

-1 
-2 
-2 

-4 
+2 

+5 

+ 37 

+41 

+102 

+ 105 

+ 109 

+94 

+ 137 

+ 120 

-37 

+ 14 

-11 
+ 117 

+86 
+ 196 
+233 

+ 143 

+208 
+470 
+560 

+645 
+ 768 
+989 

+ 1244 
+ 1282 
+ 1325 
+ 1394 
+ 1452 

+ 1460 

+ 1419 

+ 1510 

+274 

+255 

+201 

+ 144 

+ 77 

+63 

+68 

+ 180 

+ 101 

-65 

-82 

-68 

-67 
-64 
-65 
-55 
-54 
-55 






15 






Vertical Crustal Movements 



321 



Table J.— Line of lei'els, 0.4 km tvest of Bridge No. 51-35 over Topanga Creek to intersection of Foothill Blvd. and Ocean Vieiv Blvd., 

La Canada— Continued 



Location 



Bench mark 



Elevation 



Apparent 





Preearthquake 


Postearthquake 




km 


m 


m 


mm 


64.86 


327.102 


327.043 


-59 


65.36 


333.784 


333 . 708 


-76 


65.72 


329.155 


329.092 


-63 


65.81 


329.858 


329 . 794 


-64 


66.24 


333.865 


333.807 


-58 


66.70 


339.113 


339.070 


-43 


66.88 


343.695 


343.651 


-44 


67.05 


345.243 


345.199 


-44 


67.73 


351.297 


351.246 


-51 


67.75 


351.397 


351.343 


-54 


68.16 


351.608 


351.569 


-39 


68.22 


351.207 


351.181 


-26 


68.68 


368 . 1 70 


368.125 


-45 


69.23 


365.997 


365.962 


-35 


69.25 


366.638 


366.605 


-33 


70.40 


377.018 


376.922 


-96 


70.88 


402.899 


402.879 


-20 


70.98 


405.510 


405.493 


-17 


71.26 


406 . 233 


406.196 


-37 


71.33 


406.129 


406.096 


-33 


71.59 


409 . 509 


409.481 


-28 


71.81 


411.192 


411.167 


-25 


71.85 


411.462 


411.447 


-15 


72.06 


415.703 


415.689 


-14 


72.09 


415.249 


415.237 


-12 


72.22 


418.267 


418.254 


-13 


72.32 


420.484 


420.472 


-12 


72.40 


422.182 


422.172 


-10 


72.51 


422.644 


422.635 


-9 


72.73 


427.891 


427.883 


-8 


72.82 


429.421 


429.416 


-5 


72.98 


435.290 


435.287 


-3 


73.14 


442 . 357 


442 . 353 


-4 


73.17 


442.496 


442.494 


-2 


73.29 


446.932 


446.928 


-4 


73.34 


448.992 


448.986 


-6 


73.45 


454.036 


454 . 029 


-7 


73.51 


456.034 


456.027 


-7 


73.56 


457.802 


457.792 


-10 


73.62 


460.426 


460.420 


-6 


73 . 72 


464.240 


464.233 


-7 


73.87 


468.455 


468.448 


-7 


74.01 


473.208 


473.199 


-9 


74.16 


478.934 


478.926 


-8 


74.33 


483.659 


483.648 


-11 


74.40 


486.021 


486.013 


-8 


74.67 


495.565 


495.557 


-8 


74.78 


498.212 


498.204 


-8 


74.99 


506.655 


506.638 


-17 


75.07 


509.221 


509.214 


-7 


75.36 


515.802 


515.792 


-10 


75.51 


521.815 


521.810 


-5 


75.57 


521.965 


521.954 


-11 


75.78 


530.851 


530.844 


-7 


75.83 


533.462 


533.456 


-6 


76.24 


549.688 


549.683 


-5 


76.41 


554.819 


554.813 


-6 


76.46 


556.423 


556.415 


-8 


76.80 


560.092 


560.088 


-4 


77.07 


560.584 


560.581 


-3 


77.17 


559.880 


559.876 


-4 


77.52 


562 . 700 


562 . 700 





77.64 


564.003 


564.003 





77.77 


563.081 


563.081 






Hansen Lake 
(continued). 



03-00300 
03-00270 
03-00244 
03-00238 

03-00210 
03-00160 
03-00150 
03-00120 
03-00061 

03-00060 
03-00030 
03-00025 
03-00010 
02-04080 

02-04079 
02-04046 
02-04020 
02-03980 
02-03961 

02-03959 
02-02310 
02-02340 
02-03930 
02-03900 

02-03899 
02-03870 
02-03840 
02-03811 
02-03780 

02-02010 
02-03750 
02-03720 
02-03661 
02-03660 

02-03630 
02-03601 
02-03530 
02-03510 
02-03480 

02-03420 
02-03410 
02-03390 
02-03360 
02-03329 

02-03300 
02-03270 
02-03210 
02-03179 
02-03150 



Tujunga . 



02-01260 
02-03119 
RS 6 (USGS) 
09-01080 
09-01050 



09-01046 
09-01030 
09-01020 
09-01017 
09-00991 

09-00967 
09-00931 
09-00895 
09-00870 
09-00830 



CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 



CofLA) 

CofLA) 

09-01110. 

CofLA) 

CofLA) 



CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 

CofLA). 
CofLA). 
CofLA). 
CofLA). 
CofLA). 



322 



San Fernando Earthquake <>\ 1971 



Table 3.— Line of levels, 0.4 Ittn ii'rst of liritlge So. 5J-75 over Topitnga (reek to irilersei lion of I oolhill 111' 'I and Ocean \ ir„ Hi, ,i 

La Canada— Continued 



Location 



Bench mark 



IJist,i!jr ' 



.lion 



Tujunga (continued). 



09-00812 (CofLA) 
09 00811 (CofLA) 
09-00800 (CofLA) 
09-00790 (CofLA) 
09-00781 (CofLA). 

09-00750 (CofLA) 
09-00721 (CofLA) 
09-00661 (CofLA) 
09-00629 (CofLA). 
09 00600 (CofLA). 

09-00570 (CofLA) 
09 00557 (CofLA). 
09-00540 (CofLA). 
09-00530 (CofLA) 
09-00511 (CofLA). 



Preearthq •■ arthquakc 



Apparent 

■ menl 



km 
78.06 
78 10 
78.35 
78.57 
78.82 

78 98 

79.42 

80 32 
80.61 

81 .02 

81 .40 
81 .68 

82.10 
82.44 
82 . 79 



m 
558 405 

r ,47 5 18 
540 853 
531 017 

523 090 
516 333 
481 .651 

476.440 
477.945 

477. 21 5 
475 714 

464 .819 

457.121 



m 
Y,i; 40", 
558.223 
047 538 
540 855 
531 018 

523 092 
516 135 

481 652 
476.438 

477.949 

477.220 
475 719 
469.266 

464 821 
457.125 



mm 







+2 

+ 1 

-1 
-2 
+4 

+5 
+5 

+4 



47-11 (LACo)= 09-00509. 



82.81 



456 . 766 



456 769 



+ 3 



16 



Vertical Cruslal Movements 



328 



Table 4.— Line of levels, 6.5 km southeast of Ventura to San Pedro 





Bench mark 


Distance 


Elevation 


Apparent 
movement 






Preearthquake 


Postearthquake 




Ventura 


. .. X 569 


km 

0.00 

0.95 

2.44 

5.03 

6.11 

7.77 

7.80 

9.42 

10.87 

11.19, 

10.29 
11.47 
12.74 
13.38 
14.72 

15.37 
16.33 
17.76 
19.14 
20.91 

21.94 
22.69 
23.80 
26.28 
26.30 

26.31 
27.49 
27.53 
28.54 
29.90 

30.06 
30.21 
31.80 
31.99 
32.66 

33.96 
34.04 
36.09 
36 . 50 
37.70 

38.43 
38.66 
40.14 
40.70 
41.99 

43.50 
44.16 
44.99 
46.75 
48.52 

48.80 
50.33 
52.21 
54.13 
55.58 

57.00 
58.03 
58.61 
60.52 
62.23 

62.28 
63.07 
63.94 
65.43 
65.45 


m 
25.172 
24.850 
29.283 
24.033 
23.470 

21.852 
22.084 
1 7 . 560 
16.934 
15.313 

17.077 

12.998 

10.956 

9.292 

7.324 

6.340 
3.630 
4.411 
4.902 
4.701 

4.205 
4.861 
4.462 
8.451 

7.446 

8.197 
3.644 
3.632 
2.114 
1.550 

3.367 

4.021 

14.334 

17.817 

9.417 

6.159 
4.456 

10.514 
7.748 

18.392 

12.412 

12.679 

13.175 

8.959 

9.138 

31.104 
22.965 
5.625 
44.060 
29.624 

29.625 

52,886 

31.434 

5.714 

5.012 

9.145 
62.801 
49 . 220 
39.126 

5.323 

5.320 

41.197 

14.190 

5.169 

5.171 


m 

25.143 
24.828 
29.255 
24.016 
23.447 

21.823 
22.052 
17.534 
16.914 
15.294 

17.055 

12.983 

10.945 

9.284 

7.319 

6.335 
3.629 
4.397 
4.885 
4.681 

4.172 
4.822 
4.435 
8.422 
7.418 

8.168 
3.612 
3.599 
2.082 
1.518 

3.333 

3.988 

14.304 

17.787 

9.388 

6.131 
4.427 

10.480 
7.719 

18.361 

12.380 

12.646 

13.144 

8.925 

9.104 

31.072 
22.931 
5.591 
44.030 
29.591 

29.602 

52.851 

31.402 

5.682 

4.977 

9.113 
62.772 
49.195 
39.102 

5.301 

5.298 

41.179 

14.172 

5.156 

5.156 


mm 

-29 

-22 

-28 

-17 

-23 

-29 
-32 
-26 
-20 
-19 

-22 

-15 

-11 

-8 

-5 

-5 

-1 

-14 

-17 

-20 

-33 
-39 
-27 
-29 
-28 

-29 
-32 
-33 
-32 
-32 

-34 
-33 
-30 
-30 
-29 

-28 
-29 
-34 
-29 
-31 

-32 
-33 
-31 
-34 
-34 

-32 
-34 
-34 
-30 
-33 

-23 
-35 
-32 
-32 
-35 

-32 
-29 
-25 
-24 
-22 

-22 
-18 
-18 
-13 
-15 


mm 




Y 569 






H 1051 


20 




R 30 






A 570 






D 174 






X 318 






B 570 






U 318 






B 31 






V 318 






W 1100 






Y 901 






J 1051 






V 1100 






U 1100 






... L 1099 






H 584 






G 584 






F 584 Reset 1962 






M 1099 






E 584 

K 1051 






Pass RM 1 

Pass RM 2 






B 584 






Laguna 2 AZI 






A 584 






Tidal 4A 






Z 583 






R 1051 






H 1099 






Point Mugu RM 9.635. . 






G 1099 






Q 1051 

X 583 






Shale RM 

W 583 






P 1051 






M 1051 






U 583 






N 1051 






T 583 






S 583 






G 7 B (VCo) Reset 1957 






U 1051 


19 




Q583 Reset 1954 






V 1051 =48-1 50C 






W 1051 =48-149B 






R 50(USGS) =48-149 






X 1051=48-147B 






L 583=48-142 






R 49(USGS) Reset 1938 = 48-136 

K 583=48-131C 






J 583 = 48-126 






R 48(USGS) Reset 1937=48-122 

H 583=48-119 

Z 576 = 112A 






Y 576=48-107 






1307 Reset 1938=48-106 






F 9A =48-102 






G 9A = 48-100 






F 1052=48-95A 

1303 Reset 1938 = 48-95 





324 



San Fernando Earthquake of 1971 



Table i— Line of levels, 6.5 l<m toutheatl of Ventura to Sim Pedro < ontinued 



Location 


Ben< li mark 




Distt 


l.i< /atioa 
Pro arthq 




a 


Port 1 lueneme 


















(continued). 


E 1052=48 89A 

D 1052 =48 85A 






km 
66 88 
68 26 
68 95 
70. 18 
70. S 


m 
48.737 
60 M0 

27 790 
6 799 

176 


m 

48 724 

60 129 

27.728 

6.785 

163 


-13 

-11 

-02 
-14 

-15 






C 1052=48 80A 

R 576=48- 78 










48-77A (LACo) 






71 .49 
72.30 

7 ) . 62 
74.84 
76.31 


4.573 

4 222 

5 T,'< 

125 

6 632 


S60 

4.208 

', 724 

111 

6.638 


-13 

-14 
-11 
-14 






S 576=48 76 

B 1052=48 75A 

N 576 = 48 -73 

M 576 = 48 -70A 










L 576 = 48-67 

48-()6 (LACo) 






78.31 
78.63 
79.96 

82.21 
83.60 


6 623 
6 663 
8 774 
6 826 
6 K>2 


6 616 
6 654 
8.764 

6 817 

6 . 290 


-7 
-9 
-10 
-9 
-6 






P 99 Reset I'M! =48 62. . 

J 576=48-56 

11 576 = 48-50 




15 


Santa Monica 


G 50 = 48-31 

. .. F 576 =48-33 


= 48- 





86 83 
87.97 

88 84 
89.32 
89.47 


-,111 
5.731 
5.9 V, 
5 089 
7.851 


5 101 
5 723 
5.928 
5 078 
7.842 


-10 
-8 
-8 

-11 
-9 






11 767=48-34 

39 (CofLA) =48-35.. . 
Tidal Sta. 44 Tidal 4 = 






Tidal Sta. 44 Tidal 3 = 
Tidal Sta. 44 Tidal 2 = 
Tidal Sta. 44 Tidal 5 = 

L 767=48-17 

K 767=48-14 


48- 

= 48- 

:48" 


■38 

20 

18 


89.60 

89.82 
90.13 
91.46 
92.63 


7.042 
17.954 
19.585 

7.047 

6.37) 


7.032 

1 7 . 940 
19.579 

7.038 
6 . 302 


-10 
-8 

-0 

-9 

-11 


14 




E 776 = 48-11 

M 767=48-9 

N 17(CofLA)=48-8 (LACo) 

P 50 = 27-13 

S 767 = 27-12 


93.49 

94.48 

94.58 

101.62 

102.37 


3.959 
4.097 

3.282 
5 . 794 
16.6 


3.952 
4.090 
3.275 
5.781 
16.648 


-7 

-7 

-7 

-13 

-11 






R 767 = 27-10 

56.328 (CofLA) = 27-9A(LACo) 

T 767 = 27-9 

H 1052 = 27-5A 

B 768 = 27^ 


103.46 
103.83 
104.27 
105.93 
106.92 


15.162 

17.024 
15.722 

12.002 
7.432 


15.155 
17.017 
15.711 

12.053 
7.429 


-7 
-7 
-11 
-9 
-3 






27-3 (LACo) = Tidal 2 
R 50 = 27-2 

V 767 = 27-1 

Y 614=21-24 

J 1052 = 21-26A 






107.29 
107.43 
108.50 
108.96 
110.06 


4.986 
4.033 
7.230 
8.365 
10.633 


4.981 
4.030 
7.223 
8.358 
10.624 


-5 
-3 
-7 
-7 
-9 










12 




Torrance C2 = 21-28.. 
20 (USGS) = 21-29. . . 

S 50 = 21-30 

C 768 = 21-31 

Z 767=21-33 






110.88 
110.89 
110.91 
1 1 1 . 34 
112.56 


6.693 
7.180 
7.282 
8.267 

7.115 


6.680 
7.165 
7.268 
8.239 
7.097 


-13 
-15 
-14 
-28 
-18 






T 50 = 21-35 

Torrance E7A = 21-40. 
Torrance F7 = 21-42. . 






113.63 
115.46 
116.14 
116.45 
118.24 


4.693 

2.560 

5.312 

13.429 

21.181 


4.675 

2.526 

5.279 

13.397 

21.160 


-18 
-34 
-33 
-32 
-21 














RS 28A (USGS) = 21-45. . 
. . Redondo = 21-50 






Redondo Beach 








Redondo RM = 21-50A. . . 
D 768 = 21-51B 




118.28 
119.19 
119.82 


20.964 
15.050 
25.977 


20.945 
15.034 
25.962 


-19 
-16 
-15 






E 768 Reset 1962 = 21- 


52C 




10 



Strong-Motion Accelerograph Records 



CONTENTS 




Page 






326 


Accelerograph 


Network 


326 


Strong-Motion 


Results 


347 


Summary 




348 


Acknowledgments 


348 


References 





R. P. MALEY 

Seismological Field Sitmey 

Earth Sciences Laboratories 

Environmental Research Laboratories, NOAA 

W. K. CLOUD 1 

Berkeley Seismograph Station 
University of California 
Berkeley, Calif. 

i Former Chief of Seismological Field Survey 



At the time of the San Fernando earthquake, the 
Seismological Field Survey of the National Oceanic 
and Atmospheric Administration (NOAA) was oper- 
ating, in cooperation with numerous other organiza- 
tions, a dense network of strong-motion accelero- 
graphs in southern California. As a result, 241 
accelerograms were recorded during the shock, in- 
cluding more than 175 from the Los Angeles area 
where a large number of instruments are installed at 
various levels of high-rise buildings, 21 to 50 km 
from the epicenter. 

Evaluation of these data will be relevant particu- 
larly to the investigation of dynamic behavior of in- 
strumented buildings under moderate seismic forces. 
Also, in a related aspect, it may provide the best 
measure of intensity of ground motion in noninstru- 
mented areas where destruction was the heaviest. 
Perhaps information from other stations may prove 
to be equally important in completing the total pat- 
tern of strong shaking, for accelerations were re- 
corded at several dams, near aqueducts and pumping 
facilities, and at numerous free-field locations — all es- 
sentially outside Los Angeles. In any event, the total 
collection of strong-motion records, the largest ever 
compiled from a single earthquake, has provided 
more significant data than had been accumulated 
during the 39-year history of the program. The ulti- 
mate benefit derived from application of the strong- 
motion data program is a highly rewarding payoff 
for the long-range investment in engineering seismol- 
ogy investigations made by the Seismological Field 
Survey under the National Ocean Survey and the 
former U.S. Coast and Geodetic Survey. The Seismo- 
logical Field Survey was transferred to NOAA's En- 
vironmental Research Laboratories in 1972. 



Editors' note. — This paper is adapted from the report: Hudson, 
Donald E. (ed.) , Strong-Motion Instrumental Data on the San 
Fernando Earthquake of Feb. 9, 1971, Earthquake Engineering 
Research Laboratory, California Institute of Technology, Pasadena, 
and Seismological Field Survey, National Oceanic and Atmospheric 
Administration, San Francisco, Sept. 1971, 260 pp. 



325 



326 



San Fernando Earthquake of 1971 



ACCELEROGRAPH NETWORK 

Since late 1932, the Seismological Field Survey lias 
operated a strong-motion accelerograph network in 
the Western United States to record damaging mo 
tions of earthquakes. Following the establishment of 
;i group of stations in the early and middle 1930s, 
the number of instruments in southern California, 
some 15 to 20, remained relatively constant until 
1963, at which time the first modern accelerograph 
was designed and produced by United Electro-Dy- 
namics (later absorbed by Teledyne Geotech) . The 
introduction of this new instrument stimulated the 
development of an extensive cooperative network by 
the U.S. Coast and Geodetic Survey and other orga- 
nizations — such as the California State Department 
of Water Resources, U.S. Army Corps of Engineers, 
and California Institute of Technology — private 
building owners subject to seismic provisions ol local 
building codes, and various other public and private 
institutions. From 1963 to the present, the size of the 
network increased at an accelerating pace — particu- 
larly since 1965 when the city of Los Angeles passed 
an ordinance requiring three accelerographs in new 
structures taller than six stories. This recjuirement 
became more widespread when it was adopted by 
many other cities as a result of being included in the 
appendix of the 1970 Uniform Building Code. Con- 
sequently, at the time of the San Fernando earth- 
quake of February 9, 1971, there were over 200 accel- 
erographs in and near Los Angeles, 185 of which 
were in Los Angeles and Beverly Hills. 

STRONG-MOTION RESULTS 

Locations of strong-motion accelerograph stations 
in central and southern California at the time of the 
San Fernando earthquake, whether or not the instru- 
ment was triggered by ground shaking, are shown in 
successively greater geographic detail for the region 
south of Fresno (fig. 1) , the extended Los Angeles 
area (fig. 2) , and the zone of heaviest concentration 
in central Los Angeles (fig. 3) . 

Each instrument site is coded with a permanent 
identification number; thus, one may go directly to 
the listing of strong-motion instrumental data, issued 
annually by the Seismological Field Survey, to find 
the geographic coordinates, instrument type, and op- 
erating characteristics of that particular accelero- 
graph. Note that each point on the map refers only 
to the station location, whereas the accompanying 



numbei oi numbers indicate the presence ol one or 
more insti uments at thai panic ular site. 

The earthquake was recorded by five different 
types ol strong-motion accelerographs, potsesfii 
variety ol natural periods, sensitivities, and recording 

media /table I | . Foul ol the five models ! 
developed and marketed since 1963 and are, in a 
sense, largely responsible for the substantial u> 
in the network because previous instrumentation 
was bulky, difficult to maintain, more expensive, and 
required special housing. Reproductions of typical 
seismograms are shown as follows: on 12-inch paper 
records from the- \l< 240 in figures 4, 5, and 6; on 
70-mm film records lumi the SM V 1 in figure 7; and 
on 35-mm film records from the MO— 2 in figure 8. 
Representative recordings from the RFT-250 are 
shown in a paper in Volume III by Hudson, 
"Strong-Motion Accelerogram Processing." Almost 
90 pei cent ol the acceleration data were recorded on 
the newer models, including all data obtained from 
the 68 multiple-instrumented buildings. For more 
detailed information concerning characteristics of 
various models, relet to Hudson (1970) and Halver- 
son (1969 and 1971 . 

A total of 241 records were recovered from sta- 
tions located between 8 and 369 km of the epicenter, 
the majority ol records being obtained from sites 
closer than 75 km, primarily in the Los Angeles re- 
gion. Table 2 lists maximum accelerations for the 
three components at each station. It includes station 
name and locator coordinates for figures I, 2, and 3, 
epicentral distances, instrument identification num- 
bers referenced to the annual strong-motion data 
table, type of structure at each site, specific location 
of instruments within multistory buildings and 
upon dams, and general geology for each site. Where 
the notation XR appears in the data column, no 
record was obtained because of battery failure or 
equipment malfunction. Where the notation PR ap- 
pears, only a partial record was obtained and, con- 
sequently, the earliest and strongest motions of the 
earthquake were not recorded. All instruments 
within 250 km are included in the table, whether or 
not they were triggered by the earthquake, because 
the mere fact that the instrument did not receive 
sufficient ground motion to activate its starter is, by 
itself, of some importance. Figures 9, 10, and 11 
show the maximum horizontal and vertical ground 
accelerations plotted on maps at their respective 
station locations. 



Strong-Motion Accelerograph Records 327 




© 
■a 

E 

a 
C 



fee 

■S 
C 

3 

.« 
C 



2 
Q 

3 






3 

bo 



32H San Fernando Earthquake "j 1971 



34*45 



34*30 



34*15 



34*00 



33*45 



33*30' 




118*45' 118*30' 118*15' 118*00' 117*45' 

Figure 2. — Accelerograph stations in extended l.os Angeles area during San Fernando earthquake 



Strong-Motion Accclerograph Records 329 





^ 




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330 San Fernando Earthquake of 1971 

Table I .—Different accelerograph model', triggered by the Sari lerttatuto earthquake 



Instrument 


Earth- 
quake 
records 


Sensitivity 


C&GS Standard 


28 


cm/g 
6 to 17 


AR-240 

RFT-250 

MO-2 


75 
58 
45 


7.5 

1.9 

1.5 horizontal, 
2.2 vertical. 


SMA-1 


35 


1.9 



Period 



)<»-( ording medium 



Manufacture* 






Second 

0.04 6- or 12-inch photo papei Coat) an<: Purvey 

,08 

.06 12-inch photo papei Teiedyne Geotech, Im 

o r > 70-mm him Teiedyne Geotech, Jn< 

.03 35-mm him Vn tonal Engineering, Ltd , 

New Zealand. 

.04 70-mm him Kinemetrics, Inc 



1932 

1963 
1967 
1967 

1970 



The highest earthquake accelerations ever instru- 
mental ly measured, high-frequency horizontal pulses 
in the lg + range, were recorded on the east abut- 
ment of the Los Angeles County Flood Control Dis- 
trict's Pacoima Dam, 8 km south of the epicenter 
and 4 km north of the surface faulting in the Syl- 
mar-San Fernando area. The station is located on a 
jointed and fractured granitic ridge, part of a large 
block of the San Gabriel Mountains that was 
thrusted up and left laterally at least 2 m during the 
earthquake. Maximum horizontal accelerations of 
1.25g occurred 6 to 8 seconds after instrumental trig- 
gering, within a 7-second envelope of the heaviest 
ground shaking, where acceleration values generally 
ranged from 0.50 to 0.75g (see the paper in Volume 



III by Tiilunac and Hudson. Analysis ol l'a- 
coima Dam Accelerogram"). A peak vertical acceler- 
ation of 0.72g was recorded at the same time during 
an average background level ol 0.4 to 0.5g. The 
highest ground accelerations measured in the past 
were: 0.3g, recorded at Fl Centro, 8 km from the 
Imperial fault, during the magnitude 7.1 earth- 
quake of 1940 and 0.5g, recorded only 75 m from 
breakage that occurred on the San Andreas fault 
during the magnitude 5.3 Parkfield earthquake of 
1966. A comprehensive analysis of the Pacoima Dam 
record is included in the paper by Trifunac and 
Hudson, cited above. 

The next highest horizontal accelerations meas- 
ured during the earthquake were slightly less than 



8244 ORION BLVD., LOS ANGELES 



1st Fl. North r^^j^f^^^^ f,/\ 



1st Fl. Down 



•w^j^Wfifl^^ — xy^~Nw^ 



1st Fl. West ■■*wv-^w\A»ru^^ — „ ~ ■ — 



■10 seconds- 



Figure 4. — AR-240 accelerograph record from Holiday Inn, S244 Orion Boulevard, Los Angeles. 



Strong-Motion Accelerograph Records 331 



3710 WILSHIRE, LOS ANGELES 



BSM 



T West ■V/\f\J\/f^\/J^^ — *~- 



BSMT Down 



BSMT South 



10 seconds 



Figure 5- — A R-240 accelerograph record from 3710 Wilshire Boulevard, I.os ingrles. 



SANTA FELICIA DAM , CREST 



S 75° W 'i urn n fii i ffl^^/V/fyW, /VW\ Ai'Vn.Mftri 



DOWN 



/WW^Wlnr-WS. 



S 15° E 



10 seconds 



Figure 6. — AR-240 accelerograph record from Santa Felicia Dam, crest. 



0.4g, recorded at two stations 25 to 29 km northwest to 31 km, recorded maximum accelerations of 0.16 to 
of the epicenter in the Castaic area. By contrast, 0.1 9g, one-half or less than those at Castaic (refer to 
nearby instruments of the Lake Hughes array, at 29 Nos. 4, 12, 13, 14, and 16 in table 2). A superficial 



332 San Fernando Earthquake of 1971 

420 NO. ROXBURY DRIVE, BEVERLY HILLS 



10th Fl. N 50°E 



:■'■ 






10th Fl. Down — > -. "-. 



10th Fl. N 40°W 



5th Fl. N 50°E 



^V/im 'i V ^ ■ '■ '■■■l-—l»-i.^^*-W»/^/ 






5th Fl. Down — ■ w»»»»''w»vwiMM/W " » fa**tfo*t & > t *i*if**MfStiyr$i'iti*<*i&**w*w*it**'' Jl ' 
5th Fl. N 40°W ' — ~w — ~~ -^--.-. >AAJ\J\rw 

1st Fl. N 50°E ■» "» »■ ■* ■ ■ ■■ -'^>^\\/Vl) n j>WVVVW^^A^ANA/VV^ 



1st Fl. Down — ■■ 
1st Fl. N 40°W ■— 



-»^VvVW«\f\/V'vW*/\/V v VvVvAVVvy\ 



fa\/*S* - 



10 Seconds- 



Figure 7.—SMA-1 accelerograph record from 420 North Roxbury Drive, Beverly Hills. 

5260 CENTURY, LOS ANGELES 



o 

z 

"D 

c 

O CL 

,_ 3 

</> 

° * 

UJ .O 



IT o> 

o> — , 



Roof East 

Roof North 

Roof Up 



4th Fl. East 

4th Fl. North 
4th Fl. Up 



1st Fl. East 

1st Fl. North 

1st FI.Up 





I second 



Figure 8. — MO-2 accelerograph record from 5260 Century Boulevard, Los Angeles. 



inspection of these results suggests that geological 
conditions had a considerable effect upon the ampli- 
tudes because the lower values were recorded on 
crystalline rock and the higher values on Tertiary 
sandstones. Perhaps future examination of spectra 
will cast more light upon the character of this appar- 
ent amplification. 

An interesting set of records was obtained at 



United Water Conservation District's Santa Felicia 
Dam located on Piru Creek, 33 km northwest of the 
epicenter, where two accelerographs and six seismo- 
scopes were installed on the crest and at various sur- 
rounding; sites. The dam is an earthfill structure 
with a 1,260-foot-lons: crest rising; 200 feet above the 
streambed. Figure 6 shows the accelerograph record 
from the crest station where the maximum accelera- 



Strong-Motion Accelerograph Records 333 



Table 2.— Maximum accelerations recorded during the San Fernando earthquake 









Location 


Dis- 




Maximum acceleration (?) 












Identifi- 






tance 


Com- 











Structure 












Station name 


cation 






from 


ponent 


Ground 


Other 


Geology 


type 


Comments 






number* 


Map 


Key 


epi- 




level 






























center 




Floors/Levels 








1 


. Pacoima 
Dam. 


279 


2 


C-3 


km 

8 


Down . . . 
S.74°W.. 
S.16°E. . 


0.72 
1.25 
1.24 


4th 


S-roof 


Highly 

jointed dio- 
rite gneiss. 


Small build- 
ing. 


4 km from 
surface 
faulting. 


2. 


. Los Angeles, 


241-3 


2 


C-4 


20 


Down . . . 


0.17 


0.23 


0.22 


Alluvium. . . . 


7-story RC ** 


8 km from 




8244 










North . . . 


.27 


.18 


.39 




building. 


surface 




Orion. 










West 


.14 


.24 
4th 


.31 

8-roof 






faulting. 


3. 


.Los Angeles, 


458-60 


2 


C-4 


24 


Down . . . 


.12 


.19 


.17 


Alluvium 


Circular 7- 


13 km from 




15107 










West 


. 11 


.23 


.34 


500'; water 


story RC 


surface 




Vanowen. 










South . . . 


.12 


.26 


.38 


table at 70'. 


building. 


faulting. 


4. 


.Lake 

Hughes, 
No. 12. 


128 


2 


B-2 


25 


Down . . . 

N.21°E.. 
N.69°VV . 


.18 
.37 
.28 


6th 


13-rooj 


Eocene sand- 
stone below 
a shallow 
(10'±) 

layer ol 
alluvium. 


Small build- 
ing. 




5. 


.Los Angeles, 
14724 
Ventura. 


253-5 


2 


C-4 


28 


Up 

N.78°W. 
S.12°W.. 


.09 
.19 
.26 


.11 

.27 
.36 
7th 


NR 

.21 
.32 

13-rooj 


Alluvium 


12-story RC 
building. 




6. 


. Los Angeles, 


466-8 


2 


C-4 


28 


Down . . . 


.10 


.18 


.13 


Alluvium; 


12-story RC 






15250 










S.09°W.. 


.23 


.25 


.26 


water table 


building. 






Ventura. 










S.8TE. . 


.14 


.21 

7th 


.18 

13th 


at 55'. 






7. 


. Los Angeles, 
15433 
Ventura. 


256-8 


2 


C-4 


28 


Up 

N.12°E.. 
N.78°W. 


NR** 

NR 

NR 


.15 
.24 
.17 

9th 


.07 
.27 
.23 

18-roof 


Alluvium 


1 3-story RC 
building. 




8. 


. Los Angeles, 


461-3 


2 


C-4 


28 


Down . . . 


.11 


.22 


.21 


Alluvium; 


17-story St. ** 






15910 










S.09°W.. 


.13 


.18 


.22 


water table 


building. 






Ventura. 










S.81°E. . 


.15 


.13 


.23 


at 35'. 






9. 


. Los Angeles, 
16055 
Ventura. 


259-61 


2 


C-4 


28 




NR 


NR 


NR 


35' of allu- 
vium over 
siltstone 
and sand- 
stone; 
water table 
at 50'. 


12-story RC 
building. 


Midlevel ac- 
celerograph 
out lor 
repair. 


10. 


. Los Angeles, 
16661 
Ventura. 


118-20 


2 


C-4 


28 






10-root 






9-story RC 
building. 


Owner did 
not supply 
batteries. 


11. 


. Pasadena, 
Jet Pro- 
pulsion 
Laboratory 


267-8 


2 


D 4 


29 


Down . . . 
S.08°W.. 
S.82°E. . 


.13 
.17 
.21 


.21. 

.21 
.38 




Sandy-gravel . . 


9-story St. 
building. 




12. 


.Lake 

Hughes, 
No. 4. 


126 


2 


C-2 


29 


Down . . . 
S.2TW.. 
S.69°E. . 


.16 
.16 
.19 






Weathered 
granitic. 


Small build- 
ing. 




13. 


.Lake 

Hughes, 
No. 9. 


127 


2 


B-2 


29 


Down. . . 

N.21°E.. 
N.69°W. 


.12 
.15 
.16 






Gneiss 


Small build- 
ing. 




14. 


.Castaic 


110 


2 


B-2 


29 


Down . . . 
N.21°E.. 
N.69°W. 


.18 
.39 
.32 


11th 


20th 


Sandstone . . . . 


Small build- 
ing. 




15. 


. Los Angeles, 


220-2 


2 


C-4 


30 


Down 


.09 


PR** 


.23 


Interlayered 


20-story RC 






3838 










North. . . 


.18 


PR 


.10 


soft sand- 


building. 






Lanker- 










West 


.13 


PR 


.21 


stone and 








shim. 


















shale. 






16. 


.Lake 

Hughes, 
No. 1. 


125 


2 


C-2 


31 


Down . . . 
N.21°E.. 
N.69°W. 


.12 
.17 
.13 






Granitic 


Small build- 
ing. 




17. 


.Glendale, 
633 East 
Broadway. 


122 


2 


D-4 


32 


Down . . . 
S.70°E. . . 
S.20°W.. 


.14 
.28 
.23 






Alluvium 


3-story build- 
ing. 





See footnotes at end of table. 



334 



San Fernando Earthquake of li>7l 



Table 2.— Maximum acceleration* recorded during the sun Fernando earthquake Continued 









Location 


Dis- 




Maximum ai ' deration ( ?) 












Identifi- 






tant c 


( !om- 










Sti'j' 












Station name 


cation 






from 


pom m 


' rround 


Oil,., 


< ,i '. 










number* 


Map 


Key 


epi- 




level 






























ccntei 






Flooi l i 








18. 


. Los Angeles, 
Griffith 
Park Ob- 
servatory. 


141 


2 


C-4 


Km 
33 


Down . . 

South 
West 


0.12 
.18 
.16 






Granitic 


Ojn< fete pier 

on bi 




19. 


. Palmdale. . . . 


262 


2 


D-2 


33 


Down . . 

S.60°E 

S.30°W. 


.08 

.11 
.13 

Abutment 
crest 








ing. 




20. 


.Santa Felicia 
Dam. 


284-5 


2 


A 3 


33 


Down . 
S.82°W. 

S.08°E . 
Down. . 
S.75°W. 
S.15°E. . 


09 

.24 

.2', 


0.07 

.18 
.22 




Sandstone- 
shale < urn- 
plex. 


Earthfill 

darn: height 

200', 

leneth 

i,2&y. 


6 tetsa 

,rds 
also ob- 
tained on 
and near 
the dam. 


21. 


. Pasadena, 
Seismo- 
logical Lab- 
oratory. 


266 


2 


D-4 


34 


Down . 
East . . . 
South. . 


.08 
. 1') 
.11 


6th 


12-roof 


Weathered 
granitic. 


2-story build- 
ing. 




22. 


. Los Angeles, 
7080 
Hollywood. 


238-40 


3 


C-l 


34 


Down . . 
East 

North. . 


.06 
.11 
.10 


, 16 
.19 
.12 

12lh 


0.22 
.21 
.12 

22d 


Alluvium. . . . 


11 -story RC 
building. 




23. 


. Los Angeles, 
1 760 North 
Orchid. 


446-8 


3 


C-l 


34 


Up.... 

South. . 
East . . . 


.08 
.16 
.13 


.14 

.08 

.14 
7th 


.1'* 
.11 

.20 

14th 


Alluvium .... 


22-story RC! 
building. 




24. 


. Los Angeles, 


232-4 


3 


D-l 


34 


Up.... 


.09 


NR 


NR 


Alluvium; 


14-story St. 






6430 










South. . 


.19 


NR 


NR 


water table 


building. 






Sunset. 










East . . . 


.14 


NR 

6lh 


NR 

12-roof 


at 55'. 






25. 


. Los Angeles, 


235-7 


3 


D-l 


34 


Up.... 


.08 


PR 


.29 


Alluvium; 


1 1-storv St. 






6464 










South. . 


.11 


PR 


.24 


water table 


building. 






Sunset. 










East . . . . 


.12 
P.E. lot 


PR 

Base. 


.28 
Roof 


at 55'. 






26. 


. Los Angeles, 


133-5 


3 


C-l 


35 


Up 


.12 


.06 


NR 


700' ± of 


14-storv RC 






Hollywood 










East . . . . 


.22 


.15 


NR 


alluvium. 


building. 






Storage. 










South . . 


.19 


.11 
3d 
level 


NR 
8th 
level 








27. 


. Los Angeles, 


226-8 


3 


D-l 


35 


Down . . 


.13 


.13 


.20 


Shallow 


8-storv RC 


Accelero- 




4867 










S.89°W. 


.17 


.30 


.45 


alluvium 


building. 


graphs on 




Sunset. 










S.0TE. . 


.17 


.22 


.46 


over Mio- 
cene silt- 
stone. 




B and 2 in 
north wing; 
on 8 in 
east wing. 



28.. Fairmont 121 

Reservoir. 



29. .Beverly Hills, 452-4 

435 North 
Oakhurst. 

30. .Los Angeles, 142-4 

120 
Robertson. 

31. .Beverly Hills, 455-7 

450 North 
Roxbury. 

32 .. Beverly Hills, 416-8 
9100 
Wilshire. 



2 C-2 



3 B-2 



3 B-2 



3 B-2 



3 B-2 



36 



36 



Up 

N.34°W 

N.56°E. 



36 Down . 
North. 
West . . 



Down . . 
S.02°W 
S.88°E. 



37 Down . . 
N.50°E. 

N.40°W 



37 Up... 
East . . 
South. 



.05 
.10 

.07 

.04 
.06 
.09 

.03 
.09 
.09 

.04 
.20 
.17 

.04 
.16 
.12 



5th 

.05 

.13 
.14 

4th 

NR 
.18 
.18 

5th 
.10 
.22 
.21 

5th 

.08 
.13 
.15 



11 -roof 
.10 

.24 
.25 

9th 
.12 
.33 
.28 

10th 

.12 
.30 
.22 

11 -roof 

PR 

PR 
PR 



Granitic 

Alluvium; 10-story RC 

water table building. 

at 22'. 

Alluvium 9-story RC 

building. 

Alluvium 10-story RC 

building. 



Alluvium; 
water table 
at 40'. 



10-story RC 
building. 



33 . . Beverly Hills, 434-6 
9450 
Wilshire. 



3 B-2 



37 



NR 



NR 



NR 



Alluvium; 
water table 
at 40' + . 



10-story RC 
building. 



See footnotes at end of table. 



Table 



Strong-Motion Accelerograph Records 335 

2.— Maximum accelerations recorded during the San Fernando earthquake— Continued 

Location Dis- Maximum acceleration (g) 

tance Com- Structure 

from ponent Ground Other Geology tv P e Comments 

Map Key epi- level 

center Floors/Levels 

km 

3 A-2 37 Up 0.07 70' of allu- 7-story build- Instrument 

North. ... .10 vium over ing. adjacent to 

West .09 5,000' of U.C.L.A. 

sedimen- reactor, 
tary rock. 

2 D-4 37 Down.... .10 Approxi- 2-story build- 
East .11 mately ing. 

North.... .10 1,000' of 

alluvium 

upon 

granite. 

10-roof 

2 D-4 37 Down .12 0.14 Approxi- 9-story RC 

East .18 .34 mately building. 

North .22 .33 1,000'' of 

alluvium 

upon 

granite. 

3 B-2 38 NR Alluvium Small build- 

ing. 

16th 28-roof 

3 B-2 38 Up .06 PR 0.35 Silt and sand 27-story St. 

S.46°E... .08 PR .15 layers; building. 

N.44°E... .10 PR .12 water level 

at 70'. 

9th 21-roof 

3 B-2 38 Down .07 .14 PR Silt and sand 19-story St. 

N.46°W.. .12 .18 PR layers; building. 

S.44°W. . . .17 .11 PR water table 

at 70'-80'. 
Slh 16-roof 

3 B-2 38 Down .08 .16 .31 Silt and sand 15-story RC 

S.36°E... .08 .21 .28 layers; building. 

N.54°E... .10 .22 .28 water table 

at 70-80'. 

7 th 17 -roof 

3 B-2 38 Down .07 .12 .27 Silt and sand 16-story St. 

N.54°E... .11 .10 .10 layers; building. 

N.36°W.. .13 .14 .12 water table 

at 70-80'. 
Nth 20th 

3 B-2 38 Down NR .19 .35 Silt and sand 20-story St. 

N.54°E... NR .14 .15 layers; building. 

N.36°W.. NR .06 .08 water table 

at 70'-80'. 

Slh 9th 

level level 

3 B-2 38 Down NR .09 .11 Silt and sand 6-story (9- Basement 

S.36°E... NR .18 .38 layers; level) RC accelero- 

N.54°E... NR .12 .31 water table parking graph out 

at 70'-8O'. ramp. for repair. 

10th 19-roof 

3 B-2 38 Up NR NR .23 Alluvium 17-story RC 

N.50°E... NR NR .35 building. 

N.40°W.. NR NR .18 

8th 15th 

3 A-2 38 Up PR PR .16 Alluvium. 15-story RC Upper 2 

N.76°W.. PR PR .15 Water table building. instruments 

N.14°E... PR PR .20 at 55'. in elevator 

tower, 
structur- 
ally separ- 
ated from 
the north 
and south 
residential 
towers. 



Identifi- 
Station name cation 

number* 



34. .Los Angeles, 140 
U.C.L.A. 



35. .Pasadena, 475 

C.I.T. 
Athenaeum. 



36. .Pasadena, 264-5 

Millikan 
Library, 
C.I.T. 



37. .Century City, 410 

Ground 
Station. 

38. .Los Angeles, 184-6 

1900 

Avenue of 
Stars. 

39.. Los Angeles, 187-9 
1901 

Avenue of 
Stars. 

40. .Los Angeles, 425-7 

1800 
Century 
Park East. 

41 . . Los Angeles, 440-2 

1880 
Century 
Park East. 

42. .Los Angeles, 419-21 

1888 
Century 
Park East 
Building. 



43.. Los Angeles, 422-4 
1888 
Century 
Park East 
Ramp 43. 

44. .Los Angeles, 193-5 

2080 
Century 
Park East. 

45. .Los Angeles, 407-9 

930 
Hilgard. 



See footnotes at end of table. 



83(5 



Stui Fernando Earthquake <>f 1971 



Table 2.— Maximum acceleration* recorded during the s»" Fernando earthquake— A, ontimued 









La ation 


Di»- 




Maximum a< < eleratii 












Identifi- 






l.llir e 


Com- 






















Station name 


cation 






llOIII 


ponent 


Ground 


Othe 


' ,- D 










number* 


Map 


Key 


epi- 




level 






























centei 






I loon Level* 


















km 






Hth 


nth 








46. 


. Los Angeles, 
945 
Tiverton. 


178 80 


3 


A 2 




Down 

N.78°W. 

S.12°W.. 


NR 
NR 
NR 


0.10 

.12 
23 

3d 


15 

.14 

18 

f,th 


Alluvium 


1 1- ■ 
build 




47. 


. Los Angeles, 
4680 
Wilshire. 


223 5 


3 


D-2 


38 


Down. . . 

N.r. E 
N.75°W . 


0.08 

12 
09 


1 1 

.22 
.18 
16th 


16 

.24 
. 30 


Alluvium 


building 




48. 


Los Angeles, 


428-30 


3 


C 2 


38 


Up 


,03 


.08 


. 15 


Alluvium 


ry St. 






5900 










N.83°W 


.07 


.12 


17 


asphaltu 


building. 






Wilshire. 










S.07°W 


.07 


.10 

10th 


.14 

nth 


sands. 






49. 


. Los Angeles, 


443-5 


3 


C-2 


38 


Up 


'.04 


.07 


.07 


Thin layer of 


! 7-story RC 






6200 










N.08°E.. 


. 1 3 


.28 


',<) 


allu\ mm 


building. 






Wilshire. 










N.82°W. 


.13 


.15 

3d 


7th 


asphaltic 
sands. 






50. 


. Los Angeles, 


413-5 


3 


B-2 


39 


Up 


.07 


NR 


NR 


Alluvium 


Arcuate- 


>ro- 




1177 










N.31°W. 


.12 


NR 


NR 




shaped 7- 


graph on 7 




Beverly 










N.59°E.. 


.11 


NR 


NR 




story RC 


was out 




Drive. 














8th 


17-roof 




building. 


for repair. 


51. 


. Los Angeles, 


431-3 


3 


D-2 


39 


Down . . . 


.05 


.10 


.20 


Alluvium, 


1 6-story RC 






616 South 










North . . . 


.10 


.22 


. SI 


siltstone at 


building. 






Normandie 










West .... 


.11 


.14 
■1th 


.23 

S-roof 


25'. 






52. 


. Los Angeles, 
3407 West 
Sixth. 


199-201 


3 


D-2 


39 


Down. . . 
South . . . 
East .... 


.06 
.17 
.19 


.10 
.21 
.21 

2d 


.26 
.29 

.21 
12lh 


Alluvium 


7 stories; 2 
St. and 5 
RC. 




53. 


. Los Angeles, 
3345 
Wilshire. 


196-8 


3 


D-2 


39 


Down . . . 
South . . . 
East .... 


.07 
.12 
.09 


NR 

.17 
.11 

13th 


.12 
.21 
.26 

31st 


Alluvium 


12-story RC 
building. 




54. 


. Los Angeles, 


202-4 


3 


D-2 


39 


Up 


.07 


PR 


PR 


Siltstone; 


31 -story St. 






3411 










South . . . 


.11 


PR 


PR 


water table 


building. 






Wilshire. 










West .... 


.14 


PR 


PR 


at basement 
level. 






















5lh 


Uth 






55. 


. Los Angeles, 
3470 
Wilshire. 


208-10 


3 


D-2 


39 


Down. . . 
East .... 
North . . . 


.05 
.12 
.15 


.10 
.24 

.21 
nth 


.16 
.22 

.23 

21st 


Alluvium 


11 -story RC 
building. 




56. 


. Los Angeles, 


211-3 


3 


D-2 


39 


Up 


.06 


NR 


NR 


Alluvium; 


21 -story St. 






3550 










North. . . 


.18 


NR 


NR 


water table 


building. 






Wilshire. 










West 


.12 


NR 

5th 


NR 

nth 


at 35'. 






57. 


. Los Angeles, 
3710 
Wilshire. 


217-9 


3 


D-2 


39 


Down. . . 
West 
South. . . 


.08 
.17 
.16 


.10 
.27 
.16 

8th 


.17 
.37 
.22 

14-roof 


Alluvium 


11 -story RC 
building. 




58. 


. Los Angeles, 


449-51 


3 


E-2 


40 


Down . . . 


.04 


.07 


.14 


Alluvium; 


13-story RC 






2500 










N.29°E.. 


.10 


.13 


.20 


siltstone at 


building. 






Wilshire. 










N.6TW. 


.10 


.16 

7th 


.19 

15lh 


20-30'; 
and water 
table at 35'. 






59. 


. Los Angeles, 


137-9 


3 


F-2 


41 


Down . . . 


.08 


.10 


.17 


Miocene silt- 


15-story St. 






Water and 










N.50°W. 


.14 


.17 


.16 


stone. 


building. 






Power 










S.40°W.. 


.20 


.13 


.12 










Building. 














12th 


18-roof 








60. 


. Los Angeles, 


145-7 


3 


E-2 


41 


Up 


.04 


PR 


.09 


25' of allu- 


17-story RC 


Instruments 




222 South 










N.53°W. 


.15 


PR 


.40 


vium over 


building. 


in different 




Figueroa. 










S.37°W.. 


.12 


PR 


.31 


shale; 

water table 
at 20'. 




bldg. sec- 
tions; G- 
north tower 
and 18- 
south 
tower. 



See footnotes at end of table. 



Slrong-Molion Accelerograph Records 337 



Table 2.— Maximum accelerations recorded during the San Fernando earthquake— Continued 









Location 


Dis- 




Maximum acceleration (g) 












Identifi- 






tance 


Com- 










Structure 












Station name 


cation 






from 


ponent 


Ground 


Other 


Geology 


type 


Comments 






number* 


Map 


Key 


epi- 




level 






























center 






Floors/Levels 


















km 






nth 


18-roof 








Gl 


. Los Angeles, 


148-50 


3 


E-2 


41 


Up 


0.06 


NR 


0.17 


25' of allu- 


17-story RC 


Instruments 




234 South 










S.53°E. . 


.17 


NR 


.50 


vium over 


building. 


in different 




I'igueroa. 










N.37°E.. 


.20 


NR 

19th 


.44 
39th 


shale; 

water table 
at 20'. 




sections; 

C-west 

lower, 12- 

elevator 

tower, and 

18-east 

tower. 


62. 


. Los Angeles, 
445 South 
Figueroa. 


157-9 


3 


E-2 


41 


Down . . . 

N.52°W. 
S.38°W.. 


.06 
. 14 
.13 


0.12 
.21 
.13 

glh 


NR 
NR 
NR 

17-roof 


Shale 


39-story St. 
building. 




63. 


. Los Angeles, 
250 East 
First. 


151-3 


3 


F-2 


41 


Down. . . 

N.36°E.. 
N.54°W . 


.04 
.09 
.13 


.07 
.21 
.17 

16th 


.21 
.16 
.18 

32-roof 


Alluvium 


1 5-story St. 
building. 




64. 


. Los Angeles, 


172-4 


3 


E-2 


41 


Up 


.06 


.15 


.22 


Pliocene 


31 -story St. 






800 West 










N.53°W. 


.15 


.18 


.28 


siltstone. 


building. 






First. 










N.37°E. . 


.09 


.11 

6lh 


.18 
11 -roof 








65. 


. Los Angeles, 
533 South 
Fremont. 


160-2 


3 


E-2 


41 


Up 

N.30°W. 
S.60°W.. 


.08 
.25 

.22 


.16 
.34 
.31 

2d 


PR 
PR 
PR 

glh 


Alluvium 


10-story RC 
building. 




66. 


. Los Angeles, 
750 South 
Garland. 


169-71 


3 


E-2 


41 


Down. . . 
S.30°W.. 
N.60°W . 


PR 
PR 
PR 

2d 


.10 
.22 
.16 
10th 


.15 
.30 

.23 
nth 


Alluvium 


8-story RC 

building. 




67. 


.Los Angeles, 


154-6 


3 


E-2 


41 


Down . . . 


.07 


PR 


.23 


Shale and 


16-story St. 


Second floor 




420 South 










S.37°W.. 


.12 


PR 


.23 


siltstone, 


building; 


is ground 




Grand. 










S.53°E. . 


.17 


PR 


.32 


several 
1,000'. 


note com- 
ment. 


level; floor 
numbers 
from ad- 
joining 

building. 



68. .Los Angeles, 469-71 3 E-3 

1625 
Olympic. 

69. .Los Angeles, 163-5 3 E-3 

611 West 
Sixth. 

70. .Santa Anita 104 2 D-4 

Dam. 



71..Alhambra, 482-4 2 D-4 

900 South 
Fremont. 



72. Los Angeles, 437-9 3 E-3 

1150 South 
Hill. 



73.. Los Angeles, 214-6 3 E-3 

3663 
Hoover. 



74.. Los Angeles, 166-8 3 E-3 

646 South 
Olive. 



75.. Los Angeles, 175-7 3 E-3 

808 South 
Olive. 









6th 


10th 






41 


Down .... 


.16 


.14 


.23 


Alluvium 


. 10-story RC 




N.28°E.. . 


.14 


.18 


.23 




building. 




N.62°W. . 


.27 


.22 

24th 


.28 

43d 






41 


Down. . . . 


.06 


NR 


.11 


Alluvium .... 


. 43-story St. 




N.52°W. . 


.10 


NR 


.11 




building. 




N.38°E... 


.11 


NR 


.18 






42 


Down. . . . 


.07 






Granite dio- 


Small build 




N.03°E.. . 


.18 






rite com- 


ing. 




N.87°W. . 


.24 


6th 


12th 


plex. 




42 


Down .... 


.09 


.11 


.17 


Few 1 00' of 


12-story St. 




West 


.13 


.15 


.18 


alluvium 


building. 




South. . . . 


.11 


.14 
5th 


.15 
10th 


over silt- 
stone. 




42 


Down .... 


.05 


.09 


.15 


500' of 


10-story St. 




S.53°E. . . 


.12 


.11 


.14 


gravelly 


building. 




N.37°E... 


.09 


.10 


.11 


sand over 
shale. 




42 




NR 


NR 

4th 
level 


NR 

7th 
level 


400' of 
alluvium. 


7-story RC 
building. 


42 


Down .... 


.08 


.12 


.26 


Alluvium 


. 8-level RC 




S.37°W... 


.22 


.25 


.38 




parking 




S.53°W... 


.25 


.26 

4th 
level 


.48 

Hth 
level 




ramp. 


42 


Down. . . . 


.09 


.19 


.24 


Alluvium . . . . 


. 8-level RC 




S.37°W... 


.14 


.16 


.25 




parking 




S.53°E. . . 


.13 


.26 


.44 




ramp. 



See footnotes at end of table. 



338 



San Fernando Earthquake <>\ 197/ 



Tabu- 2.— Maximum acceleration* recorded during tl« Sn„ Fernando earthquake ' i,,,i,,,u,,i 







Identifi- 


Location 


Dis- 
tant e 


( JlMI- 


Maximum at celeral 
























Stc.' 




Station name 


cation 






from 


ponent 


( (round 


Othe 


' /' ology 










numb' i ■ 


Map 


Key 


epi- 




lev« 1 




























< entei 






Plooi 1 ■ 


















km 






■Ith 










76. 


. Los Angeles, 


181 3 


2 


I) 4 


42 


Down. . . . 


0.08 


0.12 


1 ', 


Pleisbx 'ii'- 








1640 










.WW AY. 


.14 


.20 


24 


alluvium; 


building 






Marengo. 










S.52°W.. . 


.14 


.26 


.44 


water table 
at ',','. 






















1th 








77. 


. Los Angeles, 


250-2 


2 


C 4 


42 


Up 


NR 


II 


16 


Alluvium; 


10-story \" 






11661 San 










N.35°W. . 


NK 


.08 


10 


water table 


building. 






Vicente. 










S.55°W... 


NR 


.09 

flh 


II 


at r rr. 






78. 


. Los Angeles, 


205-7 


3 


I. 3 


42 


Up 


.05 


.08 


09 


400' of allu- 


12-story J 


Roo' 




3440 Uni- 










S.61°E. . . 


.08 


.1 ; 


24 


\miii 


building. 


'e|e, j/ ra p}, 




versity, 










N.29°E 


06 


.14 


.26 


clay and 




is in top of 




u.s.c. 














•ith 


9th 


shale, water 
table at 
27V. 




small 
ele. ated 
penthouse. 


79. 


. Los Angeles, 


190-2 


2 


D 4 


42 


Down 


.06 


.08 


.12 


Shale at east 


9-story RC 






2011 










S.28°W... 


.08 


16 


.20 


end of 


building. 






Zonal. 










S.62 E 


.07 


.18 


.21 


building; 8' 
of hll at 
west end. 






80. 


. Pyramid 


58 


2 


A-2 


44 




NR 






Shale 


Small build- 
ing. 




81. 


. Pearblossom . 


269 


2 


E-2 


46 


Down .... 

North. . . 
West 


.06 
.10 
.15 






400' of allu- 
vium over 
14,000' of 
sedimentary 
rock. 


Small build- 
ing. 




82. 




288 


2 


D-4 


46 


Up 

S.07°VV... 
N.83°W. . 


.05 
.09 

.11 


6th 


12th 


> 1,000' of 
alluvium; 
water table 
at >300'. 


6-story build- 
ing. 




83. 


. Los Angeles, 


244-6 


2 


C-5 


48 


Down .... 


.04 


.05 


.06 


Terrace 


12-story RC 






8639 










S.45°W... 


.04 


.10 


.12 


deposits — 


building. 






Lincoln. 










S.45°E. . . 


.04 


.10 
7th 


.12 
14th 


sand. 






84. 


. Los Angeles, 
9841 
Airport 
Boulevard. 


247-9 


2 


C-5 


49 


Up 

North .... 
West 


.01 
.03 
.03 


NR 
NR 
NR 

■flh 


.05 
.10 
.09 

S-roof 


Alluvium 


14-story RC 
building. 




85. 


. Los Angeles, 
5260 
Century. 


229-31 


2 


C-5 


49 


Up 

East 

North. . . . 


.02 
.06 

.06 


.04 
.04 
.07 


.08 
.09 
.06 


Alluvium 


7-story St. 
building. 




86. 


. Whittier 
Narrows 
Dam. 


289 


2 


D-4 


52 


Down .... 
S.53°W... 
S.37°E. . . 


.05 
.10 
.10 






More than 
1,000' of 
alluvium. 


Earthfill dam; 
height 56', 
crest length 
14,960'. 


Accelero- 
graph on 
crest of 
dam. 


87. 


. Oso Pump- 
ing Plant. 


52 


2 


B-l 


55 


Down .... 
North .... 
West 


.06 
.05 
.05 






Alluvium 


Small build- 
ing. 




88. 


. Puddingstone 
Dam. 


278 


2 


E-4 


62 


Down .... 
N.55°E.. . 
N.35°W. . 


.05 
.09 
.05 






Volcanic 
elastics and 
intrusions 
with asso- 
ciated 
shales. 


Small build- 
ing. 




89. 


. Palos Verdes 
Estates. 


411 


2 


C-5 


67 


Down. . . . 
S.25°E. . . 
N.65°E. . . 


.01 
.04 

.02 






Shallow 
Pleistocene 
sands over 
shale-vol- 
canic com- 
plex. 


2-story build- 
ing. 





See footnotes at end of table. 



Strong-Motion Accelerograpli Records 339 

Table 2.— Maximum accelerations recorded during the San Fernando earthquake— Continued 









Location 


Dis- 




Maximum 


acceleration (?) 












Identifi- 






tance 


Com- 










Structure 












Station name 


cation 






from 


ponent 


Ground 


Other 




Geology 


type 


Comments 






number* 


Map 


Key 


epi- 




level - 






























center 






Floors /Levels 


















km 




§1 


§2 










90 


.Wrightwood . 


290 


2 


F-3 


70 


Down . . 
S.25°W. 
S.65°E . 


0.02 
.05 
.04 


0.02 
.06 
.04 




Alluvium 
veneer on 
igneous 
metamor- 
phic com- 
plex. 


Small build- 
ing. 


Both accelero- 
graphs at 
ground 

level. 


91. 


. Tejon 


96 


1 


C-3 


71 


Down . . 
East , . , 
North. . 


.02 
.02 
.03 






Granitic 


Small build- 
ing. 




92. 


.Long Beach, 
Terminal 
Island. 


130 


2 


D-5 


71 


Up.... 
S.69°W. 
N.21°W 


.02 
.03 
.03 






Alluvium; 
water table 
at <20'. 


Small build- 
ing. 




93. 


.San Antonio 
Dam. 


287 


2 


F-4 


71 


Up.... 
N.I5°E. 
N.75°W. 


.03 
.08 
.06 






Up to 150' of 
alluvium 
over 
granitics. 


Earthfill dam; 
height 160', 
crest length 
3,850'. 


Accelero- 
graph on 
crest of 
dam. 


94. 


Long Beach, 
Utility 
Building. 


131 


2 


D-5 


72 


Up.... 
North. . 
East . . . 


.02 
.03 
.02 






Alluvium; 
water tabic 
at 15'. 


3-story build- 
ing. 




95. 


.Long Beach, 
State 
College. 


132 


2 


D-5 


73 


Down . . 

N.76°W 
S.14°W. 


.02 
.04 
.02 






Uncon- 
solidated 
silt-sand- 
clay. 


9-story build- 
ing. 




96. 


.Grapevine, 
Tehachapi 
Pumping 
Plant. 


27 


1 


C-3 


73 


Down. . 
South . . 
East , 


.02 
.05 
.07 






15' of allu- 
vium over 
gneiss. 


Small build- 
ing. 




97. 


. Carbon 
Canyon 
Dam. 


108 


2 


E-5 


74 


Down . . 
S.40°W. 
S.50°E. . 


.04 
.07 
.07 


lo- 
west 


10- 
center 


Thin allu- 
vium over 
poorly 
cemented 
siltstone. 


Earthfill dam, 
height 99', 
crest length 
2,610'. 


Accelero- 
graph on 
crest of 
dam. 


98. 


Fullerton, 


476-78 


2 


E-5 


74 


Down. . 


.02 


.04 


0.02 


Alluvium 


10-story RC 


Both upper 




2600 










West 


.04 


.11 


.09 




building. 


accelero- 




Nutwood. 










South . . 


.04 


.13 


.15 






graphs on 
top (10th) 
floor. 


99. 


.Port 

Hueneme. 


272 


1 


B-3 


78 


Up.... 
South. . 
West . . . 


.01 
.03 
.02 


Wlh 


19th 


Alluvium 
> 1,000'. 


Small build- 
ing. 




100. 


. Orange, 


472-4 


2 


E-5 


83 


Down . . 


.01 


.04 


.08 


Alluvium 


19-story RC 






4000 West 










West . . . 


.02 


.09 


.15 


> 300' over 


building. 






Chapman. 










South. . 


.02 


.08 


.11 


shale. 






101. 


.Santa Ana. . . 


281 


2 


E-5 


86 


Up.... 
N.04°E. 
S.86°W. 


.02 
.03 
.03 






Alluvium 


3-story build- 
ing. 




102. 


. Wheeler 
Ridge. 


102 


1 


C-2 


89 


Down . . 
South . . 
East. . . 


.01 
.02 
.03 






Alluvium 
200'-300'. 


Small build- 
ing. 




103. 


. Costa Mesa . . 


114 


2 


E-6 


96 


Down. . 
South . . 
East. . . 


.01 
.02 
.04 






Terrace de- 
posits. 


18-story RC 
building. 




104. 


. Cedar 
Springs, 
Allen 


111 


1 


D-3 


98 


Down. 
S.05°W. 
S.85°E . . 


.01 
.02 
.02 






Granitic 


Small build- 
ing. 





Ranch. 

105.. Devils 

Canyon. 



116 



1 D-3 



99 



Limestone- 
gneiss com- 
plex. 



Small build- 
ing. 



Two accelero- 
graphs 
were not 
triggered. 



See footnotes at end of table. 



340 San Fernando Earthquake of 1971 

Table 2.— Maximum acceleration* recorded during the s«» Fernando earthquake— Continued 









I. in .it ion 


Di - 




Maximum ■■< • eh ration {g) 












Identifi- 






lam ' 


Corn- 


























Station name 


cation 






from 


pone hi 


f wound 




Otto 














numlxi ' 




Kry 






level 






















i pi- 






; 


















km 




















106 


. Cedar 
Springs 
Pumping 
Plant. 


112 


1 


D-3 


101 


Down 

s.;»,"\v . 
S.54°E 


0.01 
03 
.03 










Shallow 
gravelly 
alluv ium. 


.Small build- 
ing. 




107. 


. Colton 


113 


1 


D-3 


104 


Up 

I... i 
South . . . 


.03 
.04 
.04 










Alluvium 
> iOO*. 


Small build- 
ing. 




108. 


.San 

Bernar- 
dino. 


274 


1 


D-3 


104 


Down. . . 

Last 
North. . . 


.02 
05 
,04 










Alluvium 
1,000'; 

watrr table 
at 3C. 


jild- 
ing. 




109. 


. Loma Linda . 


129 


1 


D-3 


111 




PR 










Alluvium 


tory build- 
ing. 




110. 


.Santa 
Barbara 
Court 
House. 


283 


1 


B-3 


119 


Down . . . 

Last .... 
North. . 


/ 


12 








Boulder 

alluvium 
700' deep. 


2-story build- 
ing. 


d not 

available 
for scaling. 


111. 


. Maricopa 


41-4 


1 


B-2 


119 


Down . . . 


<.01 <0.01 


<0.01 i 


.01 


Poorly 


Small build- 






Array. 










S.40°W.. 

S.50°E. . 


<.01 
<.01 


<.01 
<.01 




.01 

.01 


.01 

.01 


< emented 

sandstone. 


ings. 




112. 


.San Juan 
Capistrano. 


465 


2 


F-7 


120 


Down . . . 
N.33°E.. 

N.57°W. 


.02 
.04 
.03 










Alluvium. . . . 


Small build- 
ing. 




113. 


. Bakersfield . . . 


4 


1 


B-2 


122 


Up 

South. . . 
West 


<.01 

.01 

<.01 










Alluvium 
>500'. 


Large 1 -story 
building. 




114. 


.Buena Vista. . 


11 


1 


B-2 


122 


Down . . . 

South . . . 
East .... 


<.01 
.01 
.01 












ing. 




115. 


. Perris 


270 


1 


D-4 


127 














Alluvium 
veneer over 
granitic. 


Small build- 
ing. 


Was not 
triggered. 


















Z-roof 












116. 


.Taft 


94-5 


1 


B-2 


128 


Down . . . 
N.21°E.. 
S.69°E . . 


<.01 
.02 
.01 




.02 
.01 






40' of allu- 
vium over 
poorly 
cemented 
sandstone. 


1 -story school 
building. 


Vertical com- 
ponent on 
roof is 
unreadable. 


117. 


. Santa 
Barbara, 
University 
of Cali- 
fornia. 


282 


1 


B-3 


133 


Down. . . 
East. . . . 
North. . . 


.01 
.02 
.01 










Alluvium 
veneer over 
sandstone. 


2-story build- 
ing. 




118. 


.San Onofre. . 


280 


1 


D-4 


135 


Down . . . 

N.33°E. . 
N.57°W. 


.01 
.01 
.02 










Lightly 
cemented 
Pliocene 
sandstone 
>325' 
depth. 


Small build- 
ing. 




119. 




123 


1 


E^ 


139 


Down. . . 
S.45°W. . 
S.45°E . . 


.03 
.05 
.04 










Alluvium 


Small build- 
ing. 


















Spillway 


Crest 


Aux. 


crest 








120. 


. Isabella 
Dam. 


35-9 


1 


C-2 


140 


Down . . . 
N.14°E.. 
N.76°W. 


<.01 
.01 
.01 


< 


.01 
.01 
.01 


< 


.01 
.01 
.01 


Main dam on 
granite; 
Aux. on 
granite and 
alluvium. 


Earthfill dam . 


















Cont. tower 


Aux. abut. 


























<.01 


< 


.01 


























.01 




.01 


























.01 




.01 
















See footnotes at end of table. 






Table 



Strong-Motion Accclerograph Records 341 

2.— Maximum accelerations recorded during the San Fernando earthquake— Continued 









Location 


Dis- 




Maximum acceleration 


(g) 












Identifi- 






tance 


Com- 












Structure 












Station name 


cation 






from 


ponent 


Ground 


Oth 




Geology 


type 


Comments 






number* 


Map 


Key 


epi- 




level 


































ccntei 






Floors/Levels 


















fon 




Abut. 


Crest 












121 


.Cachuma 
Dam. 


106-7 


1 


B-3 


147 




NR 


NR 






Shale 


Earthfill dam . 




122 


. Anza 


103 


1 


E-4 


178 


Down. . . . 

N.45°E... 
N.45°W. . 


0.01 
.03 
.04 








Alluvium. . . . 


Small build- 
ing. 




123. 


. Point Con- 
cepcion. 


271 


1 


A-3 


188 












Shale 


Small build- 
ing. 


Was not 
triggered. 


124. 


.Salinas Dam 


64 


1 


A-2 


209 












Sedimentary 
rock. 


Concrete dam. 


Was not 
triggered. 


125. 


.San Diego. . 


277 


1 


D-5 


216 


Up 

East 

South. . . . 


<.()1 
.01 
.01 


22,1 






Shallow 
alluvium 
(50'-100') 
over sedi- 
mentary 
rock. 


4-story build- 
ing. 




126. 


. San Diego 
Gas and 
Electric 
Company. 


275-6 


1 


D-5 


216 


Down. . . . 

East 

North. . . . 


<.01 
.01 
.01 


NR 






Shallow 
terrace 
deposits. 


22-story St. 
building. 




127. 


San Luis 
Obispo. 


83 


1 


A-2 


219 












5' of clay 
loam over 
Franciscan 
shale. 


Small build- 
ing. 


Was not 
triggered. 


128. 


.Temblor. . . . 


97 


1 


A-2 


225 







§s 






Serpentine. . . 


Small build- 
ing. 


Was not 
triggered. 


129. 


. Cholame- 
Shandon 
Array. 


13-16 


1 


A-2 


227 


Down. . . . 

N.51°E... 
N.39°W. . 


<.01 
.01 
.01 

Crest 


<0.01 
.01 
.01 

Abut. 


Cont. 


ower 


Alluvium. . . . 


Small build- 
ings. 


Nos. 2 & 12 
were not 
triggered. 


130. 


.Terminus 


98-100 


1 


B-l 


229 


Down .... 


<01 


<.01 


<0.01 


Metamorphic 


Earthfill dam . 






Dam. 










S.81°E. . . 
N.09°E... 


.01 
<01 


<01 
<.01 


< 


.01 

.01 


complex. 






131. 


. Borrego 
Springs. 


105 


1 


E-4 


230 


Down .... 
S.45°W... 
S.45°E . . . 


<.01 
<.01 
<.01 














132. 


.Superstition 
Mountain. 


286 


1 


F-5 


286 












Granitic 


Small build- 
ing. 


Was not 
triggered. 


133. 


. Imperial .... 


124 


1 


F-5 


308 






Hospital 






Alluvium. . . . 


Small build- 
ing. 


Was not 
triggered. 


134. 


.El Centra... . 


117, 


1 


F-5 


318- 


Down .... 


<.01 








Alluvium 


Small build- 


Accelero- 






412, 






324 


S.52°W... 


.01 








several 


ing. 


graphs at 






464 








S.38°E. . . 


.01 








1,000'. 




Union 
Meadows 
School and 
the Irriga- 
tion Dis- 
trict sub- 
station 
were not 
triggered. 



135.. Las Vegas, 296 
Landmark 
Tower. 

136.. Las Vegas, 302 
Inter- 
national 
Hotel. 



1 F-l 348 ± Vertical. 
N.-S.... 
E.-W . . . 

1 F-l 348± Vertical 

N.-S.... 
E.-W. .. 



<.01 


Alluvium 


.01 




.01 




<.01 




.01 




.01 





See footnotes at end of table. 



342 San Fernando Earthquake of I'Jll 

Table 2.— Maximum acceleration* recorded during the s<m Fernando earthquake- t on/muni 





tation name 


Identifi- 
cation 
number* 


1 .<» ation 


1), 

tance 
from 

cpi- 
ii nli i 


< !om- 

[JOIII III 


Maxim 

Ground 
level 


mi ,K i eli ral 
Othei 


',• - 


Strut 




s 


Map 


Key 






Flooi I ■ 














km 
















137. 


. Las Vegas, 
Bank of 
Nevada. 


305 


1 


I' 1 


348± 


Up 

N.27 1 
S.63*E. . 




<0 01 
.01 

.01 




Alluvium 






138. 


. Las Vegas, 
Univ. of 
Nevada. 


309 


1 


F-l 


348 ± 


Vertical . 
N. S... . 
E.-VV . . . 


<0.01 
,01 
.01 






Alluvium 






139. 


. Las Vegas, 
Royal Inn. 


327 


1 


F-l 


348 ± 


Vertical . 

N. S 
E. W. .. 




Top 

< 01 

.01 

01 




Alluvium .... 






140. 


. Las Vegas, 
Stardust. 


311 


1 


F-l 


348 ± 


Vertical . 

N.-S 
E.-W. 




Top 

<01 
.01 
.01 




Alluvium .... 






141. 


. Las Vegas, 
Desert Inn. 


312 


1 


F-l 


348 ± 


Vertical . 

N. S 
E.-W. . . 




Top 
.01 
.01 
.02 




Alluvium 






142. 


.Las Vegas, 
Dunes 
Hotel. 


299 


1 


F-l 


348 ± 


Vertical . 
N.-S 
E.-W . . . 


.01 
.01 
.02 


Top 

.01 

.02 
.02 




Alluvium .... 






143. 


. Las Vegas, 
Sahara. 


302 


1 


F-l 


348 ± 


Vertical . 
N.-S 
E.-W . . . 




Top(200) 

<01 

.05 

.02 


Topi 400) 

<0.01 

.02 

.02 


Alluvium 






144. 


. Las Vegas, 
Ground 
Station. 


308 


1 


F-l 


348 ± 


Vertical . 
N.-S 
E.-W. .. 


<.01 
.01 
.01 

Oil 




Intake 


Alluvium . . 






145. 


. Hoover Dam, 

Nev. 


292-4 


1 


G-l 


369 


Up 

S.45°E . . 
S.45°W.. 


house 
All traces 
<.01. 


Gallery 
show ampl 


tower 
itudes 


Several 100' 
of volcanic 
breccia 

over basalt. 


Concrete dam . 


Oilhouse is 
on abut- 
ment. 



* Refers to list in "Strong-Motion Station Instrumental Data," issued annually by the Seismological Field Survey. 
** Abbreviations: PR =partial record; NR =no record; RC = reinforced concrete; and St. =steel. 



tion was slightly greater than 0.2g, approximately the 
same as that measured at the outlet structure below 
the dam. The relatively long-period waves recorded 
at the crest, 0.6 to 0.9 second, caused the adjacent 
seismoscope with a natural period of 0.75 second to 
go off scale, while at the outlet structure, the domi- 
nant period was near 0.1 second. Consequently, com- 
paratively small amplitudes were recorded on the 
seismoscope at that site (see the paper in Volume III 
by Morrill, "Seismoscope Results") . The difference 
in frequencies is attributed to the longer period re- 
sponse of the earthfill dam in contrast to that of a 
small concrete structure with an integral 30-foot still- 
ing well embedded in a sandstone and shale complex. 
Maximum horizontal ground accelerations re- 
corded during the San Fernando earthquake are 
plotted against epicentral distance in figure 12. Su- 
perimposed on the graph are the acceleration atten- 
uation curves developed by Cloud and Perez (1969) , 
using data gathered from 19 different earthquakes 



that occurred between 1933 and 1969. It is evident 
that the more conservative attenuation curve, log 

( fl /g) = 3.5 - 2 log (D + 80) , where D is the dis- 
tance to the epicenter or to the observed faulting, 
agrees well with the data from this earthquake, ex- 
cept for the unexpectedly high values at Pacoima 
Dam and smaller deviations noted at distances of 25 
and 29 km in the Castaic area. The Pacoima Dam 
anomaly may be difficult to assess because the instru- 
ment is located on a fractured granitic ridge, part of 
a regional block that was thrust up and laterally a 
few meters during the earthquake. Note that the 
data at distances greater than 45 km are consistent 
with the less conservative of the two curves, log 

(fl/g) = 2 log (D 4- 43) ; although some of the val- 
ues between 30 and 45 km do fall above that limit. 
these represent only 10 percent of the large number 
of points in that interval. 

The ground accelerations recorded in various lo- 
calities throughout the Los Angeles area, between 21 



Strong-Motion Accelerograph Records 343 




344 San Fernando Earthquake of IV7I 



34M5 



34*30' — 



.05,. 06 










10, 


.05 
7,. 12 






", 


,14 




16 


.12 
37,. 


11 




<> 



K 



i * i . ' t : r I . 



13, .08 



•AlMDAll 



.39, .1 






34*15 



34*00 



33*45' 



33*30' 




.'•'-. .02 



118*45' 118*30' 118*15' 118*00' 117*45' 

Figure 10. — Maximum horizontal and vertical ground-acceleration values in extended Los Angeles area during San Fernando earthquake. 



Strong-Motion Accclerograph Records 345 







SM6 Snn Fernando Earthquake oj 1971 









a ® 












1 


00 


- 
















- 








- 


log (o/g) = 3.0 - ! log lt> 43! ""• 




. 


• 






3 




- 


B 








MtU 






| 





*NJ ^^ 




z 


< 




- 








. 1 • 








u 












•' v :i 


• ^v ^\ 






< 








B 


® 


• •• • 








z 












• •!• 


• \^ 






o 


.10 










wdt 








o 




- 








X 


\ 






< 




. 








I 




























z 




m 








• 


• 






o 


















N 


















s 




" 








• • 

























X 


















s 

3 












• • • 










MAXIMUM ACCELERATION VALUES 












s 


















X 

< 






Three Slotioni Neorest The Epicenter 






• • • • • 

•« 


• 


"\ \ 


s 






(5) Distonce from Ihe epicenter 
3 Distance from lurfoce foulting 
All Other Stolions 






• 
• •••••• 










• 


• Distonce from the epicenter 






# * 


"• 


\ * \ 






... 


■ 






Miles 










1 






l 









Kilo-eters 
DISTANCE FROM THE EPICENTER OR FAULT 



Figure 12. — Maximum horizontal ground accelerations recorded during Sun Fernando em thqwike lvalues > 0.0] g*. 



and 42 km of the epicenter, show a surprisingly simi- 
lar range of values regardless of where the individual 
instrument clusters were located (table 3) . For in- 
stance, the maximum ground accelerations in San 
Fernando Valley, at 21 to 28 km of the epicenter, 
ranged from 0.11 to 0.27g, while those in downtown 
Los Angeles, at 41 to 42 km of the epicenter, ranged 
from 0.09 to 0.27g. Although there are considerably 
more records available from downtown Los Ansreles, 
it should be pointed out that the average of all maxi- 
mum ground accelerations was 0.1 Ig in the San Fer- 
nando Valley compared to 0.1 5g in the downtown 
area. Of additional interest, the highest amplitudes 
in the San Fernando Valley were predominantly in a 
north-south direction, nearly 90° to the trend of 
faulting. Similar strongly polarized amplitudes were 
observed on some seismoscope records recovered 
from the same area. Beyond 45 km, the apparent at- 
tenuation of peak acceleration fell off sharply as in- 



dicated by the highest values near Los Angeles air- 
port (in the 48- to 49-km distance range) of only 
0.03 to 0.06g, and at Long Beach (nominally 70-km 
distant) where the maximum accelerations were 0.02 
to 0.04g. 

Strong-motion seismograms were recorded on the 
top floors of 57 high-rise buildings in the Los Ange- 

Table 3.— Range of maximum horiuintal ground accelerations at 
various Los Angeles localities 





Distance 


Maximum 


Number 


Locality 


from 


horizontal 


of 




the 


ground 


measure- 




epicenter 


acceleration 


ments 



km g 

San Fernando Valley 21-28 0.11-0.27 10 

Hollywood 34 . 10- . 22 12 

Pasadena (C.I.T.) 37 . 10- .22 4 

Beverlv Hills-West Los Angeles . . 36-38 .06-. 20 24 

Wilshire District 38-39 .09-19 18 

Downtown Los Angeles 41—42 .09- .27 26 

Los Angeles International 

Airport 48^9 .03-. 06 6 

Long Beach 67-72 .02-. 04 8 



les area, including six reinforced concrete structures 
where upper level accelerations exceeded 0.4g — an 
eight-story hospital in Hollywood, two eight-level 
parking ramps and two 16-story towers in downtown 
Los Angeles, and a seven-story hotel 3 km east of 
downtown (Nos. 27, 60, 61, 74, 75, and 76 in table 
2) . A maximum acceleration of 0.50g, the highest 
observed in any building during the San Fernando 
earthquake, was measured in one of the 16-story 
towers. Horizontal accelerations greater than 0.3g oc- 
curred in 14 other structures, all but two of rein- 
forced concrete frame construction. Vertical accelera- 
tions exceeded 0.3g on the top floor of only three 
buildings, all located in Century City adjacent to 
Beverly Hills (Nos. 38, 40, and 42 in table 2) . 

Where ground amplitudes in buildings were equal 
to or greater than 0.1 Og, the ratio of peak horizontal 
accelerations, top to bottom, ranged from 1.1 to 2.3 
in 80 percent of the comparisons. A few buildings 
showed ratios as high as 3.5, and, at five other sites, 
ratios were less than 1.0 (0.6 to 0.9), thus showing 
an apparent reduction of seismic forces at the tops of 
the structures. These latter buildings were all 15 to 

22 stories in height, with fundamental periods of vi- 
bration between 1.5 and 2.7 seconds (Nos. 15, 23, 41 
(both directions) , and 59 in table 2) . 

As in past earthquakes, accelerograms from the 
upper floors of high-rise buildings showed the struc- 
tures responded in a manner related to their funda- 
mental and other modes of vibration (figs. 4, 5, 7, 
and 8) . Ambient vibrations were measured in nu- 
merous buildings before the San Fernando earth- 
quake, thus making it possible to compare these val- 
ues with the periods induced by seismic forces and 
with the natural periods following the earthquake 
(see Volume I paper by Mulhern and Maley, "Build- 
ing Period Measurements Before, During, and After 
the San Fernando Earthquake") . 

A summary of the types of structures existing at 
accelerograph sites reveals that nearly 80 percent 
(189) of the 241 records were obtained at various 
levels of taller buildings (table 4) . Another 29 rec- 
ords were from hydraulic structures, principally 
dams, where one to five accelerographs had been in- 
stalled in various configurations on the dam and its 
appurtenances and at the abutments. The remaining 

23 records are from accelerographs in small build- 
ings, chiefly along the San Andreas and San Jacinto 
fault zones. Perhaps the most notable deficiency in 
network coverage is the lack of free-field instruments 



Strong-Motion Accelerograph Records 347 

Table 4.— Types of structures where records were obtained 

Large buildings* Number of records from 

different levels 

Number of stories ; 

Lowest Middle Top 

Large 1 2 1 

2-4 8 

5-10.'...: 24 22 23 

11-20 28 22 29 

21-30 4 1 2 

>30 5 3 3 

Totals 71 48 58 

Hydraulic structures 

Crest of earthfill dams 7 

In concrete dam 

Intake towers 

Abutments or near dams '2 

Other existing or planned structures 6 

Total 29 

Other sites 

Arrays across the San Andreas fault 10 

Other faultline stations 7 

Miscellaneous 6 

Total 2 3 

* Excludes 1 2 Las Vegas stations. 

in the Los Angeles area, that is, there were only 
three operating accelerographs in buildings small 
enough to be called free-field stations, and just one 
of these was near the major clusters of tall buildings 
(Hollywood Storage, No. 26 in table 2) . In an 
engineering sense, the distribution of accelerographs 
was relatively inequitable because there were no re- 
corders in single-family residential dwellings, in 
moderate-size apartment units, at bridges or along 
freeways, in industrial plants or major utility sites 
(other than high-rise buildings) , or at the numerous 
harbors and marinas. 

SUMMARY 

Strong-motion accelerograph records were ob- 
tained from 241 instruments operated as part of the 
NOAA cooperative network between 8 and 369 km 
of the San Fernando earthquake epicenter. More 
than 175 of these records came from the Los Angeles 
area where building codes in a number of cities have 
required the installation of accelerographs at three 
levels in new buildings taller than six stories. 

Among the more significant results are the follow- 
ing: 

1 The highest earthquake accelerations ever 
measured, 1.25g horizontally and 0.72g vertically, 
were recorded on the abutment of Pacoima Dam, 8 
km from the epicenter. 

2 Except for the anomalously high Pacoima 



348 



San Fernando Earthquake of 1971 



Dam results, attenuation of maximum horizontal 
ground accelerations from .ill recording sites is, foi 
the most part, consistent with the equation, log 
(ajg) = ,'5. r > 2 log (I) + 80), calculated by 
Cloud and Perez for past earthquakes. 

3 The range of maximum ground accelerations 
recorded at different localities in the Los Angeles 
area was relatively similar, generally about 0.10 to 
0.2. r )£, although the measured values fell off rapidly 
beyond 45 km. 

4 Peak accelerations exceeding 0.3g were re- 
corded on the top floors ol 20 different high-rise 
buildings, including a 17-story tower 41 km from the 
epicenter where a maximum of 0.5g was observed. 

5 In 80 percent of the buildings where the 
base accelerations were 0.1 Og or greater, the top-floor 
accelerations were 1.1 to 2.3 times those recorded at 
the ground level. 

6 It is apparent that the distribution of ac- 
celerographs in southern California is far from equi- 
table, both geographically and in an engineering 
sense, because about 85 percent of the instruments 
are in the Los Angeles area and nearly all of these 
are in high-rise buildings. 

The unprecedented number of accelerograph rec- 
ords obtained from the San Fernando earthquake 
provides such a large volume of instrumental strong- 
motion data that scientists and engineers will require 
many years of investigation and research to utilize 
the data in their entirety. Since 1940, the El Centro 
record, with a maximum acceleration of 0.3g, has 
been a prime tool for use in earthquake engineering. 
Now ground accelerations have been recorded in ex- 
cess of l.Og at a site near Los Angeles and from 0.2 
to 0.4g at 14 other nearby stations. The ultimate 
evaluation of these data unquestionably will have a 
large influence upon the design and construction of 
buildings and other critical facilities, on the zoning 
of potentially high seismic risk areas, and on a host 
of other related problems. The saturation of strong- 
motion accelerographs in the Los Angeles area, 
though far from optimum, has resulted in excellent 
dividends, particularly in view of the short-term ex- 
istence of this concentrated network. 

ACKNOWLEDGMENTS 

The authors appreciate the substantial contribu- 
tions provided by their coworkers from the Seismo- 



logical Field Survey NOAA in the collection and 
handling of records, including C I Knudson, B J. 
Morrill, E. C. Etheredge P. N Mori I. J I 

and IV I. Silverstein; and special thanks to 
who completed the- painstaking task of scaling the 
records. R. }. Dielman of the- California Institute ol 
Technology supplied extensive- assistance- during the 
field investigations, in the recovery and processing ol 
records, and in the production of maps and tables 
used in this report. |. West of the- Environmental 
Research Laboratories' Spec ial Projects Party in I^as 
Vegas, New, participated in the collection of records 
and directed the postearthquake building pe-iiod 
measurements. J. I). Patterson of the Jet Propulsion 
Laboratory, California Institute ol Technology, 
drafted the instrument location maps. 

REFERENCES 

Allen, Clarence R., Engcn, G. R.. Hanks, Thomas C, Nord- 
quist, f. M.. and Thatcher, W. R.. "Main Shock and Larger 
Aftershocks of the San Fernando Earthquake, February 9 
Through March 1, 1971," The San Fernando, California, 
Earthquake of February 9, 1971 , Geological Survey Profes- 
sional Paper 733, U.S. Geological Survey and the National 
Oceanic and Atmospheric Administration. U.S. Department 
of the Interior and U.S. Department of Commerce, Wash- 
ington, D.C., 1971. pp. 17-20. 

Cloud, W. K., and Perez. \ '.. "Strong Motion — Records and 
Acceleration." Proceedings of the Fourth World Conference 
on Earthquake Engineering, Santiago, Chile, January 13-18, 
1969, Vol. I A-2, Impeso en Editurial Univesitaria, Santiago, 
Chile, 1969, pp. 119-132. 

Halverson. H. T., Some Recent Developments in Strong-Motion 
Seismographs, Geotech-A Teledyne Co., Monrovia, Calif., 
1969, 18 pp. and tables and figs. 

Halverson, H. T., "The SMA-1 Strong-Motion Accelerograph," 
Fourth Symposium on Earthquake Engineering, November 
11-16, 1970, Roorkee, India, Sarita Prakashan Nauchandi 
Grounds, Meerut, India, 1971, pp. 45-50. 

Hudson, Donald E., "Ground Motion Measurements," Earth- 
quake Engineering. Prentice-Hall, Inc., Englewood Cliffs, 
N.J., 1970^ pp. 107-125. 

Kamb, Barclay. Silver, L. T., Abrams, M. J.. Carter, B. A., 
Jordan, Thomas H.. and Minster, J. Bernard, "Pattern of 
Faulting and Nature of Fault Movement in the San Fer- 
nando Earthquake," The San Fernando, California, Earth- 
quake of February 9, 1971, Geological Survey Professional 
Paper 733, U.S. Geological Survey and the National Oceanic 
and Atmospheric Administration, U.S. Department of the 
Interior and U.S. Department of Commerce, Washington, 
D.C., 1971, pp. 41-54. 



A Statistical Summary 

of Accelerograph Performance 



R. P. MALEY 

Seismological Field Survey 

Earth Sciences Laboratories 

Environmental Research Laboratories, NOAA 



The magnitude 6.4 San Fernando earthquake of 
February 9, 1971, triggered 272 accelerographs in 
California and Nevada. Thus, it provided an authen- 
tic test for a large portion of the strong-motion net- 
work that is operated cooperatively by the Seismolog- 
ical Field Survey and other organizations in the 
Western United States. Because this earthquake was 
the first to be recorded by such a large number of in- 
struments, it is particularly relevant to examine the 
success achieved in maintaining the dense network of 
instruments that now exists in southern California. 

Table 1 shows that of the 272 accelerographs trig- 
gered by the earthquake, 229 records were obtained 
and 43 records (or approximately 16 percent) were 
lost. Table 1 also shows that the number of lost rec- 
ords was greater at code stations (19 percent) , where 



Table 1.— General accelerograph performance 




Code Noncode 
stations stations 


Total 


Accelerographs triggered 186 86 

Records obtained 150 79 

Records lost 36 7 


272 

229 

43 


Percent lost 19 8 


16 







accelerographs were installed because of building 
code requirements, than at noncode stations (8 per- 
cent) . Reasons for the disproportionately higher loss 
of records at code stations in relation to noncode sta- 
tions are: (1) the existence of a large number of 
slightly less reliable accelerographs in the code net- 
work; and (2) the greater attention, in terms of 
service interval and comprehensive maintenance, 



Editors' note. — This paper is adapted from the report: Hudson, 
Donald E. (ed.) , Strong-Motion Instrumental Data on the San 
Fernando Earthquake of Feb. 9, 1971, Earthquake Engineering 
Research Laboratory, California Institute of Technology. Pasadena, 
and Seismological Field Survey, National Oceanic and Atmospheric 
Administration, San Francisco, Sept. 1971, 260 pp. 



349 



350 San Fernando Earthquake <>\ 197/ 

given to the instruments at noncode stations. Foi 
results of accelerograph performance ai individual 
stations refer to "Strong-Motion Instrumental Data 
on the San Fernando Earthquake ol Feb. '), 1971" 

(Hudson 1971). 

There was a greater emphasis on maintenance al 
noncode stations because this portion ol the network, 
although geographically far less dense, supplies data 
at key structures and free-field ground sites, ine luding 
those along important fault] ines. These noncode sta- 
tions generally provide the seismic information 
needed to interpret variations in strong-motion re- 
sponse characteristics over a broad range of geologic 
environments. 

The accelerographs at Las Vegas, Nev., were ex- 
cluded from consideration in this report because 
they are operated by the Environmental Research 
Laboratories' Special Projects Party primarily to 
monitor nuclear detonations at the Nevada Test Site. 

Table 2, listing the specific reasons for instru- 
mental failures, shows that more than two-thirds ol 
these failures resulted from inadequacies of the power 
supply. 

Table 2.— Cause and number of accelerograph failures 

Number 
Cause of failure of 

failures 

Battery discharged * 30 

Film transport failure 6 

Relay failure 3 

Miscellaneous 4 

Total 43 

* Includes normal battery degradation (23), trickle charger plug 
pulled out ( 1 ), battery disconnected ( 1 ), battery case broken ( 1 ), 
wrong-type batteries (3), and corrosion (1). 

Five types of accelerographs operating in southern 
California at the time of the San Fernando earth- 
quake briefly are described as follows: 

1 Standard Coast and Geodetic Survey strong- 
motion seismograph, developed in 1931, is operat- 
ing today with some modifications. It requires a 
trickle charger and greater maintenance than any 
modern accelerograph. 

2 AR-240 is a compact accelerograph, devel- 
oped with external calibration capability, that is sim- 
ple to maintain but still requires a trickle charger. 

3 RFT-250, which followed the AR-240, is 
more compact, is easily maintained, and contains re- 
chargeable batteries without a trickle charger. 

4 SMA-1 is a very compact unit that operates 
with disposable batteries, thereby eliminating a 



trickle chargei 01 periodic battery recharging It is 
easily serviced and maintained. 

5 MO 'l is a coinp;ic i urnt with no cl 
needed, bui cannot be calibrated aftei installation. It 
is difficult to sei\icc- effectively and therefore oper- 
ates with a redu< ed reliability. 

Table 3 summarizes the- performance of the var- 
ious accelerograph models during the- San Fernanda 
c-ar thquake. 

Table 1.— Accelerograph performance by instrument type 

Type of Accelcro- Recordi Records \jom 

lerograph graph* lost 

Percent 
C&GS Standard 19 16 3 10 

AR 240 82 75 7 

KM 250. 66 58 8 12 

MO 2 67 V> 22 

SMA I 38 3 B 

Totals 272 229 43 16 

It is readily apparent that the failure rate is rela- 
tively low for lour types of accelerographs and inor- 
dinately high for the fifth type, the MO-2. Although 
the MO-2 is generally somewhat less reliable than 
the other instruments, it is only fair to point out 
that its failures more often were marked by longer 
intervals between inspections (table 4). The MO-2s 
were relegated by a priority system to the least 
important of the current instrumentation because of 
a number of recurring, and as yet unsolved, func- 
tional problems as well as the lack of calibration ca- 
pability after installation. Table 4 shows that the 
MO-2 inspection interval averaged 7 months and 
that the code stations generally had a much longer 
inspection interval than the noncode stations. Under 
optimum conditions, the accelerographs should be 
serviced every 2 months; in any event, servicing 
should occur at a maximum of every 3 months if 
nominal success is to be achieved in obtaining earth- 
quake records. 

The second section of table 4 shows why the rela- 
tively large loss ratio occurred among the MO-2 ac- 
celerographs: that is, the replaceable batteries had 
been in use on an average of 8i/^ months, 214 
months longer than desirable. Neglecting: the 
SMA-ls that had short-term batteries because of re- 
cent installations, it may be noted the average age of 
replaceable batteries in the code stations was nearly 
double that of noncode stations. 



1 Subsequent SMA-1 accelerographs have rechargeable batteries with 
trickle chargers. 



Summary of Accelerograph Performance 351 



Table 4.— Inspection interval before the earthquake 

Code stations Months 

MO-2 7 

AR-240 6 

RFT-250 4 

SMA-1 2V 2 

Average for all four 5% 

Noncode stations 

Average of all stations 3]/£ 

Replaceable battery age on February 9, 1971 
Code stations 

MO-2 %y 2 

RFT-250 $y 2 

SMA-1 iy 2 

Noncode stations 

Average of all stations 3}^ 



No reference was made to the standard accelero- 
graphs or AR-240s because both instruments have 
trickle chargers; consequently, batteries are not ex- 
changed on a routine basis. 

The following comments summarize the general 
results of strong-motion accelerograph performance 
during the San Fernando earthquake: 

1 Approximately 16 percent of the potential 
data from 272 instruments was lost. In contrast, dur- 
ing the Borrego Mountain earthquake of April 
1968, less than 1 percent of the data from 115 accel- 
erographs was lost. 

2 Because a greater importance was attached to 
the inspection and upkeep of the noncode instru- 
ments, a considerably larger percentage of records 
was obtained from them than from the code instru- 
ments. 2 



3 Seventy percent of the 43 records lost re- 
sulted from power supply failures — in most instances 
caused by the normal degradation of rechargeable 
batteries. With this fact in mind, it is recommended 
that all future instrumentations include trickle 
chargers to maintain the batteries whenever a con- 
venient 110-volt supply is available at the station. 3 

4 Although there appears to be a large differ- 
ence in the performance of the various accelerograph 
models, this difference, more than likely, is the con- 
sequence of the priority system of maintenance. 

5 Redundancy of time and starting systems 
among accelerographs in multiple installations is 
highly desirable because it provides individual tim- 
ing and starting capabilities to each instrument in 
event of the malfunction of one or more accelero- 
graphs within the group. A few total failures and nu- 
merous records without a time base were observed 
during the San Fernando event because of the lack 
of such compensating systems. The Seismological 
Field Survey has for a number of years recom- 
mended inclusion of alternate time systems on all in- 
struments and backup starters in multiple installa- 
tions. Had there been no redundant starters in Los 
Angeles buildings, an additional 14 records would 
have been lost. 

Because future earthquakes in California in the 
magnitude 6 to 7 range will probably trigger several 
hundred strong-motion accelerographs, it is hoped 
that these comments will provide some beneficial 
contribution to the cooperative network. 



2 The priority system of maintenance is no longer in effect. All 
instruments are now being inspected on a routine basis. 



3 Trickle chargers have since been installed on all network 
insti uincnls. 



Seismoscope Results 



CONTENTS 

Page 

353 Introduction 

353 Description of Seismoscope 

354 Seismoscope Record Recovery 
354 Seismoscope Data 

354 Records of Special Interest 

364 Acknowledgments 

364 Rf.ffrence 



B. J. MORRILL 

Seismological Field Survey 

Earth Sciences Laboratories 

Environmental Research Laboratories, NOAA 



INTRODUCTION 

At the time of the San Fernando earthquake, the 
Seismological Field Survey was operating 150 seismo- 
scopes and over 250 strong-motion accelerographs in 
the affected area. 

The seismoscope network was established in 1960 
when a number of instruments were purchased by 
different agencies, both private and governmental, 
and were installed and subsequently maintained by 
the Seismological Field Survey. 

All but six of the 150 seismoscopes in the shaken 
area recorded data useful to earthquake engineers. 
This report presents the basic data from the seismo- 
scopes. 

DESCRIPTION OF SEISMOSCOPE 

The seismoscope was designed by the U.S. Coast 
and Geodetic Survey and developed by the Califor- 
nia Institute of Technology in the late 1950s, and 
the first 200 were installed in 1960. At present, there 
are 375 in the field, scattered from Fairbanks, 
Alaska, to El Centro, Calif. The seismoscope was de- 
signed as a simplified, low-cost instrument to supple- 
ment the more expensive strong-motion accelero- 
graph. 

The seismoscope consists of a free conical 
pendulum that can move in any horizontal direction. 
The wire-flexure pivot support of the pendulum 
moves with the ground, and the resulting angular 
deflections — relative to the instrument frame — are 
recorded by a scriber on a smoked spherical watch 
glass. Eddy current damping is provided by an alu- 
minum disk in the form of a segment of a spherical 



Editors' note. — This paper is adapted from the report: Hudson, 
Donald E. (ed.) , Strong-Motion Instrumental Data on the San 
Fernando Earthquake of Feb. 9, 1971, Earthquake Engineering 
Research Laboratory, California Institute of Technology, Pasadena, 
and Seismological Field Survey, National Oceanic and Atmospheric 
Administration, San Francisco, Sept. 1971, 260 pp. 



353 



354 



San Fernando Earthquake of 1971 



shell, which moves between the poles ol a permanent 

magnet system. This aluminum segment is the prin- 
cipal contributor to the moment of inertia ol the U 
compound pendulum. Because the motion in a hori- 
zontal plane is traced as a permanent record, tlie se 
quence of events can be followed even though there 
is no time-recording device. This instrument, using a 
simple recording technique, is superior to one that 
indicates maximum displacements. 

The instrument is shown in figure 1, and a typical 
installation is shown in figure 2. Two types of 
seismoscopes now in use are the Wilmot and the 
Sprengnether, which have the characteristics given in 
table 1. 



SEISMOSCOPE RECORD RECOVERY 

Of the 150 possible records, 144 usable records 
were obtained. Six records were lost because of mois- 
ture and vandalism. Two records (Pacoima and Dry 
Canyon) were partially destroyed when the earth- 
quake motion exceeded the design limits of the in- 
struments and the recording plates were dislodged. 




W 




figure 2. — Typical teismoscope field installation Stowing 
concrete base and external protective cover. 

Table 1.— Seismoscope characteristic! 

Wilmot Spr<-nj?- 

nether 

Serial number 100 2 , Vt) 

and 500 

Sensitivity (cm rad) 5.4 r ) 6.00 

Period (seconds) 

Damping (percent of critical) 8.22 




Figure I. — The seismoscope is a relatively low-cost instrument that 
measures directly one point on the response spectrum. 



However, some useful information on these records 
was obtained during the first few seconds. 

SEISMOSCOPE DATA 

Figure 3 is a map showing the seismoscope sites in 
southern California. The site location numbers 
shown on the map are listed in table 2. The map in 
fiarure 4 shows the largest vectors of each seismo- 
scope response. For each record, the maximum dis- 
placement of the trace from the initial zero point 
was measured. From the sensitivity of the seismo- 
scope in cm rad, the maximum relative displacement 
response-spectrum value Sa was calculated from: 

pT 2 In 

S d = 7—7 m ax4/ 777 (Hudson and Cloud 1967) 

47T~ J ID 

where 

T — period (second) 
«= damping (percent of critical) 
<t>m ax = trace amplitude sensitivity. 

RECORDS OF SPECIAL INTEREST 

The records in figure 5, Nos. 213 and 210 from 
the east abutment and crest of the San Fernando 



Seismoscope Results 355 







356 



San Fernando Earthquake of 1071 



Table 2.— Southern California leitmoiCOpe stations and data from San Fernanda "fir 



\.<>> ation from 
epu ■ 



Maxin 
rdai 



City 



Building or site 



Altadena: 

Devils Gate Reservoir (crest) 

Devils Gate Reservoir (left bank) 

Residence, 1972 Sky view Drive 

Arcadia: 

Santa Anita Reservoir 

Arrowhead: 

U.S. Forest Service 

Azusa: 

Cogswell Reservoir (crest) 

Cogswell Reservoir (right bank) 

San Gabriel Reservoir (crest) 

San Gabriel Reservoir (left bank) 

Beverly Hills: 

Lower Franklin Canyon Reservoir (west abutment). . . . 

Lower Franklin Canyon Reservoir (main crest) 

Burbank: 

Burbank I ligh School 

Castaic: 

North Station 

Old Ridge Route 

Cedar Springs: 

Strong-Motion Station 

Cholame: 

Cholame Array No. 2 

Cholame Array No. 5 

Cholame Array No. 8 

Claremont: 

Live Oak Reservoir (crest) 

Live Oak Reservoir (left bank) 

Thompson Creek Reservoir (crest) 

Thompson Creek Reservoir (left bank) 

Eagle Rock: 

Eagle Rock Reservoir (west abutment) 

Eagle Rock Reservoir (main dam crest) 

El Centra: 

Imperial Valley Irrigation District (accelerograph site). 

El Centro High School 

El Centro Steamplant 

El Centro Water Works 

El Segundo: 

Hyperion Treatment Plant 

Encino: 

Encino Reservoir (crest) 

Encino Reservoir (west abutment) 

Encino Reservoir (tower) 

Glendale: 

Herbert Hoover High School 



Glendora: 

Big Dalton Reservoir (crest) 

Big Dalton Reservoir (left bank) 

Grapevine: 

Tehachapi Pumping Plant (north site) 

Tehachapi Pumping Plant (accelerograph site). 
Hollywood: 

Hollywood Reservoir (west abutment) 

Hollywood Reservoir (main dam crest) 

Hollywood Reservoir (crest) 

Hollywood Reservoir (right abutment) 

Lake Hughes: 

Lake Hughes Array: 

No. 1 (never installed) 

No. 2 

No. 3 

No. 4 

No. 4a 



Site 

no. ' 


Jut/ U 

men) 
no. 


Map 

\<>< a- 

tion 






plat en 
Dii 




Din 
tson 
(N-C.W.)« 


Dr- 


St 








O 


bn 




crn 


IK, 
147 

2 52 


566 
568 

117 


E 1 
1. 1 
I. 1 


1 50 
1 59 
151 


51 4 
51 4 


047 
074 


1 22 
1 29 


148 


565 


C 3 


124 


42.1 






149 


107 


D 3 


10 5 


105 9 




78 


150 

101 
102 
1 5 '- 


507 
530 
506 


D-3 

D ', 
D \ 
D 3 


1 1 5 
115 
114 
114 


4'5.0 
4 5 
04 4 

04 4 


088 
50 5 
3 5 1 

5 0;; 


1 12 
79 
3 27 
0.16 


1 54 


207 
200 


D 2 
D 2 


182 
182 


■ 


172 

174 


1 OS 


[56 


125 


D-I 


104 


24 9 


278 


4.85 


157 
158 


229 
2874 


C-3 


'510 
306 


2 5 ', 

29 . a 


190 


3.72 
3.88 


159 


2807 


D 5 


098 


99 . 


022 


0.29 


15 
18 
21 


2855 

2858 
2890 


A-2 
A-2 
A-2 


310 
310 
310 


208 1 
208 . 1 
208.1 


240 
315 
115 


08 
08 
0.16 


161 
162 

163 
164 


524 
514 
500 
515 


D-3 

D-3 
D-3 
D-3 


115 
115 
114 
114 


08.0 
08.0 
69.6 
69.6 


010 
2 52 
026 

030 


0.24 
0.38 
0.75 
0.35 


173 

174 


208 
209 


E-2 
E-2 


147 
147 


30.2 
36.2 


270 
300 


4.17 
4.93 


108 
169 
170 
171 


132 
158 
164 

124 


F-5 
F-5 
F-5 
F-5 






Negligible 
Negligible 
Negligible 
Negligible 




172 


102 


C-A 


183 


52.6 


090 


0.62 


165 
166 
167 


199 
217 
200 


C-3 
C-3 
C-3 


201 
201 
201 


30.2 
30.2 
30.2 


185 
178 
140 


1.59 
0.51 
1.94 


177 


141 


E-l 


156 


28.2 


Off 
center 
( vandal- 
ized,) 




178 

179 


520 

567 


D-3 
D-3 


115 
115 


60.0 
60.0 


100 

174 


0.35 
0.32 


35 
36 


2851 
2954 


C-3 
C-3 


327 
327 


72.7 
72.7 


187 

240 


0.35 
0.51 


182 
183 


205 
198 
221 
212 


D-2 
D-2 
D-2 
D-2 


168 
169 
160 
168 


31.8 
31.8 
36.6 
36.6 


320 
275 
112 
360 


1.05 
0.66 
3.44 
2.40 


186 
187 
188 
189 


2824 
2887 
2891 
2889 


C-3 
C-3 
C-3 
C-3 
C-3 


349 
347 
345 
343 


30.5 
29.4 
29.1 
29.2 


160 
080 

326 
330 


1.56 
1.44 
1.91 
2.37 



See footnotes at end of table. 



Seismoscope Results 357 

Table 2.— Southern California seismoscope stations and data from San Fernando earthquake— Continued 



City 



Building or site 



Site 
no. ' 


Instru- 
ment 
no. 


Map 
loca- 
tion 


Location from 
epicenter 


Maximum 

relative 

displacement 


Direc- 


Direc- 



tion Dis- tion Sa 

(N-C.VV.) 2 tance (N-C.W.) 2 



Lake Hughes — continued: 

Lake Hughes Array — continued: 

No. 5 

No. 6 (station removed) 

No. 7 

No. 8 

No. 9 

No. 10 (never installed) 

No. 1 1 

No. 12 

Lancaster: 

Fairmont Reservoir (south abutment) 

Fairmont Reservoir (main dam crest) 

Long Beach: 

Municipal Building (accelerograph site) 

San Pedro High School 

Terminal Island (accelerograph site) 

Los Angeles: 

Baldwin Hills Reservoir (east abutment) 

East Los Angeles Junior College 

Hancock Park 

Taylor Residence 

Colton (accelerograph site) 

Hollywood Storage (accelerograph site) 

Tauxe Residence 

Edison Building (accelerograph site) 

Vernon (accelerograph site) 

Leeds Residence 

U.C.L.A. (accelerograph site) 

Duke Residence 

West Los Angeles Public Library 

Van Nuys High School 

Southgate High School 

Elysian Heights School 

Playa Del Rey School 

Windsor Hills School 

Museum of Science and Industry 

Compton School Administration Building 

Huntington Park City Hall 

Narbonne High School 

Maricopa: 

Station B 

Monrovia: 

Sawpit Canyon Reservoir (right bank) 

Sawpit Canyon Reservoir (crest) 

Mount Wilson: 

Caltech Seismograph Station 

Pacoima: 

Pacoima Dam 

Pasadena: 

Eaton Wash Reservoir (base) 

Eaton Wash Reservoir (crest) 

Gilman Residence 

Caltech Campus, Millikan Library (accelerograph site). 

Caltech Campus, Athenaeum 

Motta Residence 

Muir High School 

Washington Junior High School 

Seismological Laboratory 

San Raphael School 

Garfield School 

Hale School 



km 



190 


2894 


C-3 
C-3 


191 


2822 


C-3 


192 


2890 


C-3 


193 


2892 


C-3 

C-3 


194 


2819 


C-3 


195 


2893 


C-3 


175 


211 


C-3 


176 


216 


C-3 


196 


147 


C-4 


197 


122 


C-4 


198 


149 


C-4 


199 


192 


D-3 


200 


104 


F-2 


201 


140 


D-2 


202 


110 


F-2 


203 


143 


D-4 


204 


146 


D-2 


205 


156 


C-4 


206 


150 


E-2 


207 


148 


E-3 


208 


123 


C-4 


209 


137 


F-2 


210 


109 


C-3 


212 


113 


C-2 


213 


139 


C-l 


214 


129 


C-4 


215 


162 


E-2 


216 


127 


C-4 


217 


154 


C-4 


218